Speciality
Spotlight

 




 


Obstetric & Gynaecology


 

 




Cervical
Ultrasound

  

  • Griff
    Jones, Darryl Maxwell (Division of Perinatology,
    Ottawa General Hospital and Fetal Medicine Unit
    Guy’s and St.Thomas’ Hospital, London)


    Cervical Ultrasound in Pregnancy 


    Prog. Obstet & Gynaec, 14, p.80

      


    The uterine cervix undergoes considerable
    physiological, biochemical and anatomical changes
    during the transition between the antenatal and
    intrapartum periods. Digital examination
    consistently underestimated length by more than
    13mm. In contrast, ultrasonographic measurements
    correlated well with those obtained using a ruler on
    the postoperative specimen.

      


    Transabdominal ultrasound

    The average cervical length to be between 35-40mm.
    Up to 6mm dilatation at the internal os was normal
    with no significant cervical change seen from the
    10th to the 36th week of gestation.

     


    115 women with risk factors for cervical
    incompetence were studied. Patient management was
    largely based on clinical (as opposed to ultrasound)
    findings. Of the women with evidence of moderate
    cervical weakness on ultrasound, one-third were
    found to have clinically normal cervices. With
    expectant management, 75% delivered before 34 weeks’
    gestation. Most of the remaining two-thirds,
    underwent cerclage with 25% delivering before 34
    weeks.

     


    Riley et al report a 50% risk of preterm birth in
    women co-incidentally found to have cervical
    shortening and membrane funneling on transabdominal
    scanning.

     



    Transvaginal ultrasound:


    Brown et al suggest that adequate cervical images
    were more likely to be obtained by transvaginal
    scanning than by transabdominal U.S.G. The cervix
    could be visualized transvaginally 99% of the time.
    When transabdominal and transvaginal cervical length
    measurements from the same woman were compared,
    transabdominal measurements were on average 5mm
    longer, presumably secondary to bladder filling. Of
    the 30 women, 29 demonstrated an increase in
    cervical length with increasing bladder volume.
    Confino et al also reported cases in which
    quantified bladder filling or manual pressure
    exerted via the transducer led to significant
    reductions in internal os dilatation in patients
    with suspected incompetence.

     


    Digital examination only assesses that portion of
    the cervix below the vaginal wall. Goldberg et al
    found the mean cervical lengths in 43 pregnant women
    measured by transvaginal ultrasound (39mm) to be
    over twice as long as those measured digitally
    (19mm) by experienced examiners. Similarly, Sonek et
    al found that digital measurement of cervical length
    showed a poor correlation with vaginal
    ultrasonography.

      



    Safety and acceptability:


     


    Heath et al questioned 100 consecutive women about
    the acceptability of a transvaginal scan at 23 weeks
    gestation: 94% experienced no, or minimal,
    discomfort only and 98% reported no or only mild
    embarrassment. Half of the women found it to be less
    uncomfortable than a speculum examination.

     


    Normal values for cervical length

    There appears to be no clinically significnat
    difference between the mean cervical lengths of
    primiparous and multiparous women.

     


    It is possible that ethnic differences in cervical
    length exist. The work of National Institute of
    Child Health and Human Development Maternal-Fetal
    Medicine Unit Network has shown a short cervix (£
    25mm) to be significantly more common in high risk
    women.

      



    DIAGNOSTIC ROLE


    Preterm Labour

     


    Murakawa et al studied 32 women presenting with
    threatened preterm labour. None of the 15 women with
    cervical lengths greater than 30 mm delivered
    preterm. If the cervix was less than 30mm, 65%
    delivered preterm and all early births were
    identified. All women with a cervical length below
    20mm delivered preterm.

     


    Gomez et al developed the term cervical index to
    include information about endocervical length and
    funnel length in a single figure. Funneling was
    present in 58% of women and associated with a nearly
    3-fold increase in the risk of preterm birth. A
    complex statistical analysis suggested that a
    cervical index ³0.52, cervical length < 18mm,
    funnel length > 9mm and funnel width > 6mm
    were all significantly associated with preterm
    birth. All the patients who delivered preterm had a
    funnel present.

     



    Cervical anatomy


    The ability to diagnose (or exclude) placenta
    praevia is one of the main benefits ascribed to
    antenatal ultrasound. Provided that the placental
    edge is at least 20mm from the internal os, a
    vaginal birth appears safe.

     



    Cervical incompetence


    Cervical conization may iatrogenically predispose to
    cervical incompetence.

     


    Management Role

    Assessment of risk of preterm birth

    Cervical length

     


    3000 women of mixed-risk were screened at both 24
    and 28 weeks of gestation. The mean cervical length
    was approximately 35mm and the overall incidence of
    spontaneous preterm birth £ 35 weeks’ gestation was
    4.3%. There was a clear inverse relationship between
    cervical length and risk of preterm birth. A short
    cervix (£ 25mm) was associated with an 8%
    probability of spontaneous preterm delivery £ 35
    weeks gestation in low-risk parous women. In
    high-risk women, this probability climbed to 31%
    with the same cervical measurement.

     


    The second study was carried out at a single inner
    city centre in the UK. Results from cervical scans
    at 23 weeks’ gestation were blinded unless the
    length was less than 16mm. A cervical length of £
    15mm at 23 weeks’ gestation carried a risk of
    spontaneous delivery £ 32 weeks of 50% and
    correctly identified 58% of these births.

      


    The third study was from a well-defined geographical
    area in Helsinki, Findland with a 99% white
    population. The mean cervical length was just over
    40mm and a short cervix was defined as one £ 29mm,
    corresponding to the 3rd centile.

     


    All three studies confirm the ability of
    transvaginal cervical ultrasound to reliably
    stratify women by risk of spontaneous preterm birth.
    Even more importantly, the background or pre-test
    risk of spontaneous preterm birth must be taken into
    account when interpreting cervical sonograms.

     



    Membrane funneling


    If the funnel length was greater than the length of
    closed cervix below it, 75% of patients delivered
    before 37 weeks’ gestation. A funnel width exceeding
    15mm was another risk factor. Heath et al found that
    all women with a cervical length £ 15mm exhibited
    funneling compared to only one-third of those with a
    cervical length of 16-25mm.

     



    Dynamic changes.


    Sonek subsequently reported the same phenomenon in
    women not believed to have cervical incompetence,
    using transvaginal scanning. He stated that the
    funneling could be accentuated or brought on by
    gentle manual pressure on the uterine fundus and
    advocated this as an ‘internal os stress test’.

     


    At present, transfundal pressure cannot be
    standardised. More recently, reports have appeared
    advocating the use of a postural challenge, with the
    cervix being scanned first while the mother is
    supine and then when upright.

     



    Cervical cerclage:


    The final report of the MRC/RCOG Multicentre
    Randomised Trial of Cervical Cerclage suggested
    benefit in only 4% of cases with prior clinical
    uncertainty. Detailed inspection revealed that
    cerclage improved outcome only after three or more
    previous very early deliveries. The mean interval
    between cerclage removal and delivery was 2.3 weeks.

     



    Cerclage placement


    Both Andersen et al and Quinn reported all the
    McDonald sutures in their series to be in the middle
    third of the cervix. The optimal placement of a
    suture was obtained in the single patient that was
    treated with a Shirodkar-type cerclage, involving
    preliminary dissection of the anterior vaginal wall.

     


    Post cerclage follow up

    Between 25-30% of patients developed funneling above
    the cerclage.

     



    Twin pregnancies


    Goldenberg et al scanned 147 twin pregnancies at 24
    and 28 weeks’ gestation. A cervical length of less
    than 25mm was twice as common in twin pregnancies as
    in singletons and became more common as gestation
    advanced, occurring in 18% of women at 24 weeks and
    33% at 28 weeks.

     



    Cervical ultrasound and routine antenatal care


    Although Zalar suggested that knowledge of
    transvaginal cervical ultrasound measurements can
    lead to a reduction in spontaneous low birth-weight
    deliveries, it cannot yet be concluded that cervical
    ultrasound has a place in routine antenatal care in
    low-risk pregnancies.

     


    Preterm prelabour rupture of the membranes

    The authors were unable to demonstrate a significant
    relationship between cervical length and the number
    of days to spontaneous labour.

     



    TECHNIQUES FOR CERVICAL SCANNING


    Transabdominal

    Cervical images are best obtained transabdominally
    with a full bladder. Unfortunately, this is
    associated with artificial lengthening of the cervix
    and potential closure of a dilated internal os.
    Therefore, it will lead to false reassurance in some
    cases. The external os can also be difficult to
    identify transabdominally. In the studies of Varma
    et al, an inflated Foley catheter balloon was placed
    against it to overcome this problem.

      



    Transvaginal


    This remains the gold standard for cervical imaging.
    Sonek et al have advocated the use of a probe with a
    240° scanning field, this would appear to be
    unnecessary. Pressure on the cervix can falsely
    increase the measured length and obscure funneling
    at the internal os. Failing to appreciate that not
    all cervical canals follow a straight line can lead
    to underestimates of length. At least 3 measurements
    should be taken and the shortest (not the average)
    used. Most authors advise scanning over
    approximately 5 min to detect dynamic changes. The
    presence of a funnel should be noted and funnel
    width and length recorded. Some authors have
    reserved the term ‘funnel’ for membrane protrusions
    greater than 5mm down the endocervical canal,
    referring to anything less as ‘nippling’.

     



    Transperineal scanning


    A glove-covered 3.5MHz or 5 MHz sector or
    curvilinear transducer is applied to the perineum to
    visualize the cervix. It is reportedly easily
    tolerated by patients, but is best performed before
    digital or speculum examination which, by
    introducing air into the vagina, produce artefact.
    The technique has been particularly useful in cases
    of prolapsing membranes when cerclage is not being
    undertaken. The contrast provided by the funnel or
    membranes usually allows excellent visualization and
    serial monitoring. Transperineal ultrasonography may
    prove to be an acceptable mass screening technique.

     



    CONCLUSIONS:


     


    As proposed by Iams et al, ultrasound imaging
    suggests cervical competence to be a continuous
    variable. Infection has attracted considerable
    interest as one of the most important aetiologies
    behind preterm labour and delivery. A weak or short
    cervix could offer less resistance to ascending
    infection. Half have positive amniotic fluid
    cultures. 

     


    Iams et al have recently reported that a cervical
    length of less than 25mm at 24 weeks’ gestation is
    strongly associated with subsequent perinatal
    infection. Bacteria can ascend the genital tract
    attached to motile sperm. Antibiotics may play just
    as important a role as cervical cerclage in
    preventing prematurity. As prostaglandins are
    implicated in the process of cervical ripening,
    non-steroidal anti-inflammatories such as
    indomethacin may have role for ultrasonographic
    cervical change, at least before 28 weeks’
    gestation. Cervical ultrasound undoubtedly allows a
    far better assessment of risk than clinical
    examination.

     


  • Frank Johnstone (Department of Obstetrics and
    Gynaecology, University of Edinburgh UK)


    Drug Use in Pregnancy


    Progress in Obstetric and Gynaecology vol.14

     


    This article is about a broad range of drugs which
    have some psycho-active properties and which are
    used for non-therapeutic reasons in pregnancy.

     


    All the drugs (with the possible exception of
    benzodiazepines) appear to have a common final
    pathway. They all act by increasing dopamine
    release. But for all of them, the common end-point
    where dopamine is released forms part of a circuit
    known as the brain reward system, consisting of a
    small group of nerve cells extending from the
    ventral tegmental area of the midbrain to limbic
    areas such as the nucleus accumbens, with
    projections to the pre-frontal cortex. The markedly
    reduced activity in the brain reward circuits on
    withdrawal also explains dependence.

     


    Over the past few decades, use has spread to most
    countries of the world. This is due partly to a
    general increase in use of psycho-active drugs,
    improvements in communication and transportation and
    the globalisation of the world economy. Indeed,
    tobacco companies have used international trade
    agreements to open up markets in the developing
    world, and the same factors facilitating trade in
    legal goods also facilitate trade in illicit drugs.

     


    Many women, who do not acknowledge any problem with
    their drug pattern, may present for the first time
    to the health care system because of the pregnancy.
    This presents a window of opportunity for harm
    minimisation and education. Pregnancy can be a great
    motivator. Drug use in pregnancy is already known to
    be a major public health problem.

     



    Some Effects of Drugs on Pregnancy


    Effects in animal studies (often with high doses)
    may be due to maternal toxicity rather than direct
    effects on the fetus (e.g. drug induced anorexia).
    There may be selection bias based on obvious chaotic
    drug use, so that the women studies are quite
    unrepresentative of population use. The small
    numbers studied may be inadequate to study
    infrequent events. Because of editorial and reviewer
    bias there may be preferential publication of
    studies which report harmful effects. Many drug
    users are polydrug users and this makes it difficult
    to isolate the effect of one drug. There are major
    problems in separating the effects of drug use from
    the other adverse personal, psychological and social
    circumstances in which drug use is taking place.

     



    Opioids


    Injecting street heroin is dangerous and in most
    cohorts of users the mortality is at least 1% each
    year. The commonest cause of death is respiratory
    depression due to overdose. The other major medical
    complications relate largely to non-sterile
    injecting, resulting in transmission of hepatitis B,
    and most importantly hepatitis C and HIV.

     


    There is no convincing evidence that opioids cause
    fetal abnormalities.They probably have a small
    inhibiting effect on fetal growth, though this is
    less than the effects of smoking. In all large
    studies, there is a modest increase in perinatal
    mortality due to preterm delivery and late pregnancy
    stillbirth, but it is uncertain how much of this
    drug is a drug effect rather than due to the effect
    of other variables. Preterm labour does seem to be
    more common in women injecting drugs rather than
    taking orally, possibly related to a higher risk of
    alternation between intoxication and withdrawal with
    relatively short acting injected drugs. An increase
    in meconium staining of the liquor is also
    consistently reported, related to episodes of fetal
    drug withdrawal.

     


    There is a high rate of neonatal abstinence syndrome
    (NAS), ranging from 50-90% in women taking opiates
    daily. Symptoms may last for weeks or even months in
    a mild form. Typically, babies feed poorly and have
    tremor on handling, a shrill cry, sneeze and may
    have watery stools. Untreated, they can develop
    projectile vomiting and electrolyte disturbance,
    seizures and coma. 

     


    The largest study of 1760 cases of sudden infant
    death syndrome, showed a 7 times increased risk with
    maternal methadone use and a 5 times increased risk
    with heroin use. 

     


    Drug effects, and the consequences of an unstable,
    impoverished environment, are very difficult to
    disentangle, but this remains an area of concern.

     



    Cocaine.


    As well as its central action, this drug has
    important peripheral effects on inhibition of
    re-uptake of noradrenaline in presynaptic nerve
    terminals. Catecholamines diffuse from the nerve
    terminals and the resulting high vascular levels
    cause vasoconstriction, tachycardia, hypertension
    and perhaps uterine contractility.

     


    The vasoconstrictive properties of cocaine raise the
    possibility that there might be fetal damage during
    episodes of fetal ischaemia or subsequent
    reperfusion. However, the overall population risk
    for users does not seem very high, perhaps because
    only those with high dosage at key gestations are
    vulnerable. A large number of studies in women are
    consistent in reporting a decrease in birth weight.
    Preterm delivery is common and, although it is very
    difficult to adjust for multiple co-variates this is
    probably also a direct drug effect.

     



    Nicotine


    Of the 4000 compounds in tobacco smoke, there is
    good evidence that nicotine is the key drug of
    addiction and nicotine, carbon monoxide and cyanide
    are thought to have the greatest adverse effect on
    the fetus. World-wide, this is the most harmful drug
    for pregnancy.

     


    There are well documented increased risks of
    spontaneous abortion, ectopic pregnancy, placenta
    praevia, placental abruption, preterm premature
    rupture of the membranes and preterm delivery. Birth
    weight is depressed by about 250g, with an increased
    risk of significant intra-uterine growth
    restriction. Intrauterine death in late pregnancy is
    more common. Overall, at least in the US, smoking
    causes an estimated 20-30% of the low birth weight
    rate and 10% of fetal and infant mortality.
    Postnatally, maternal milk production is reduced by
    about 30%. There are strong relationships with
    sudden infant death syndrome; respiratory disease
    and hospital admission in the first year of life;
    and an ongoing effect on respiratory disease in
    childhood. There are small effects on physical,
    mental and behavioural development of the child, of
    uncertain clinical significance.

     


    There may be other long-term complications.
    Potentially carcinogenic tobacco metabolites are
    present in the first urine of babies whose mothers
    smoked in pregnancy. The babies of women who smoke
    were found to have a much higher frequency of a
    genomic deletion event that is commonly found in
    leukaemia and lymphomas of early childhood.

     



    Benzodiazepines


    Diazepam overdose in 25 pregnancies was not
    accompanied by obvious fetal problems. Withdrawal
    may occur in the neonate, typically with
    irritability and slowness to feed and respond. There
    may be ‘floppy infant syndrome’ with poor suck,
    feeble cry, hypotonia, and sometimes poor
    temperature control.

     



    Cannabis


    Most studies have not reported an association
    between prenatal marijuana exposure and
    morphological abnormalities of the baby.

     



    Amphetamines


    Data currently available do not allow any accurate
    estimate of risk.

     



    Designer drugs


    The most widely used drugs at present are
    amphetamine analogues. Ecstasy (3,4
    methylenedioxymethyl amphetamine, MDMA) is one
    derivative related chemically to both amphetamines
    and hallucinogens.

     



    Alcohol


    This is the only one of these drugs which is proven
    to be teratogenic. Fetal alcohol syndrome (FAS) has
    been reviewed in a previous issue of this series. A
    wide range of other alcohol-related birth defects
    appear to occur with heavy drinking. These adverse
    effects have been well documented with very high
    maternal intakes. Judging by animal experiments,
    alcohol may affect fetal brain development at any
    gestation. Threshold effects on subsequent reading,
    spelling and arithmetic abilities in children have
    been reported at low intakes.

     


    Volatile substances

    The commonest substance is cigarette lighter refills
    (butane) but a wide range of products are used.

      



    OPTIONS FOR DRUG MANAGEMENT


    Many women who are not truly dependent on their drug
    will stop spontaneously as soon as they know they
    are pregnant. This applies to 15-20% of women who
    smoke, to many women who use ecstasy or cannabis
    episodically and it is also true of some controlled
    users of opiates.

     


    It is said that most girls who smoke 3 cigarettes as
    adolescents will become dependent, with an average
    duration of dependence of 40 years. Sadly, having
    been recruited in adolescence, half of all smokers
    die because of the habit, one-third of them before
    the age of 65 years. 20% of all deaths in developed
    countries are caused by smoking: an enormous human
    cost which can be completely avoided.

     


    Therefore, antenatal care should include advice to
    stop smoking, with easy access to programmes to
    support those who choose this. Brief intervention by
    family doctors is effective. Cutting down is
    probably not a useful aim. 

     


    Trying to persuade the woman to stop drugs may
    simply alienate her, lead to return to a more
    chaotic drug use pattern, and result in
    non-attendance for antenatal care. Therefore, the
    different options of detoxification, substitution
    and maintenance and other aspects of damage
    limitation need to be considered with full
    understanding of the woman’s aspirations and
    particular social and psychological circumstances.

     


    For most women who are dependent and who have a
    long-standing opiate habit, substitution and
    maintenance is usually the preferred option. The
    drug of choice is methadone linctus. Methadone
    maintenance treatment has been extensively
    researched, and has been shown to be effective.
    Substitution should be prescribed as part of a
    package including social and psychological support.

     


    Acute detoxification in pregnancy is not often
    appropriate but should be an option. The risks of
    withdrawal have probably been exaggerated in the
    past, and can be minimised by appropriate drug
    therapy to the mother. Detoxification can be carried
    out in the mid-trimester quite safely and this has a
    place in overall management.

     


    Slow reduction may be preferred by some women for
    opiates, and is necessary for benzodiazepines.

     


    Much of the management of drug misuse is damage
    limitation rather than cure, and in patients who
    continue to inject, it is essential to ensure that
    they have access to clean equipment, by needle
    exchange.

       


    Maternity Care in Drug Users

    Another important obligation on community care staff
    is effective liaison and communication with other
    agencies. Nothing is so guaranteed to reduce
    confidence as different agencies giving out
    different messages.

        


    The opiate using woman should be warned that
    neonatal abstinence syndrome may occur, that her
    dose is not a reliable predictor, that it can
    present after several days and can last for weeks.
    She needs also to know that NAS is usually easily
    manageable.

       


    Repeated non-sterile injection over years destroys
    peripheral veins, often leaving track marks (thrombosed,
    fibrosed veins). Occasionally there may be concern
    about the ability of the woman to look after her
    child. Many women worry that their baby may be taken
    away into care purely because they use drugs.

       


    Occasionally, there maybe incidents involving
    violence or the threat of violence, most often
    caused by the partner or visiting friends in
    hospital.

       


    Adequate pain relief can be obtained with opiates
    although much more frequent injections are likely to
    be needed. Because of the high fear about pain which
    many drug users have, epidural anaesthesia may be
    very useful.

        


    Naloxone must not be used to reverse opioid induced
    respiratory depression in the newborn because of the
    risk of precipitating an acute opiate withdrawal
    crisis.

        


    After delivery, a chart scoring for neonatal
    abstinence syndrome is helpful for all concerned.
    This is, of course, only one aspect of assessment.
    Withdrawing babies can usually be treated without
    drug management, with lots of cuddling, small
    frequent feeds, and patience. Babies may need
    neonatal unit care to maintain hydration and may
    need sedation. The logical drug is simply
    replacement of opiate, and neonatal morphine
    solution can be used.

          

  • Alessandro Ghidini, Nicola Strobelt, Anna Locatelli, Eloisa Mariani, Maria Giovanna Piccoli, and Patrizia Vergani

    Isolated Fetal Choroid Plexus Cysts : Role of Ultrasonography in Establishment of the Risk of Trisomy 18

    Am J. Obstet Gynecol April 2000, Volume 182, Number 4, Pgs. 972-977

        


    Objective – The significance of isolated choroid plexus cysts found by ultrasonographic scan during the second trimester as a marker for trisomy 18 is 

    still debated. We analyzed our data and reviewed the series published in the English-language literature to calculate the likelihood ratio of trisomy 18 in the presence of isolated choroid plexus cysts; that is, the factor by which the individual risk of trisomy 18 is increased in the presence of isolated choroid plexus cysts.

        


    Study Design – Likelihood ratios were calculated as ratio of the sensitivity to the faise-positive rate. Sensitivity was defined as the rate of isolated choroid plexus cysts detected at midgestation among fetuses with trisomy 18. False-positive rate was defined as the rate of choroid plexus cysts detected at midgestation in the population without trisomy 18. The sensitivities of all published series reporting rates of choroid plexus with trisomy 18 and in low-risk populations were included in the analysis. To these we added all cases of trisomy 18 diagnosed at our institution during the period January 1, 1988, through June 30, 1998, in which prenatal ultrasonographic examination was performed between 14 and 24 weeks’ gestation. 

       


    Results – The prevalence of second-trimester ultrasonographic detection of isolated choroid plexus cysts among fetuses with trisomy 18 was 6.7% [ 13/194]. Whereas that in the population without trisomy 18 was 0.9% [752/79, 583]. The likelihood ratio associated with isolated choroid plexus cysts was therefore 7.09 [95% confidence interval, 3.97 -12.18]

       


    Conclusion – The presence of isolated second-trimester choroid plexus cysts increases the base risk of trisomy 18 by a factor of 7.09. This likelihood ratio can be multiplied by the risk calculated according to maternal age to obtain the individual risk of trisomy 18 and thus permit more accurate counseling of the patient.


        

  • Karim D. Kalache, Roland Wauer, Harald Mau, Rabih Chaoui, and Rainer Bollmann

    Prognostic Significance of the Pouch Sign in Fetuses with Prenatally Diagnosed Esophageal Atresia

    Am J. Obstet Gynecol April 2000, Volume 182, Number 4, Pgs. 978-981

       


    Objective – Esophageal atresia may be diagnosed prenatally by ultrasonographic visualization of the blind-ending esophagus during fetal swallowing, which is referred to as the pouch sign. Our purpose was to determine whether this sign can be used to predict outcomes of affected fetuses. 

       


    Study Design – Four cases of esophageal atresia diagnosed in our center during the past 2 years were analyzed, in conjunction with 3 cases from published series. Ultrasonographic features of the pouch sign were categorized according to localization.

       


    Results – In the neck pouch group [ n=3] 1 fetus died in utero and 1 died before a corrective operation could be undertaken. In the only fetus of this group to survive a staged repair was necessary because of a long atretic gap. Conversely, 3 of the 4 fetuses with a mediastinal pouch survived after a successful corrective operation, and primary repair was possible in all cases.

       


    Conclusions – The base of the proximal blind-ending esophagus can be clearly localized by means of ultrasonography. Our data suggest that a neck pouch may be associated with an adverse outcome. This information may be useful in counseling parents when esphageal atresia is diagnosed prenatally.


         

      



 

 

Speciality Spotlight

 

 

Cervical Ultrasound
  

  • Griff Jones, Darryl Maxwell (Division of Perinatology, Ottawa General Hospital and Fetal Medicine Unit Guy’s and St.Thomas’ Hospital, London)
    Cervical Ultrasound in Pregnancy 
    Prog. Obstet & Gynaec, 14, p.80
      
    The uterine cervix undergoes considerable physiological, biochemical and anatomical changes during the transition between the antenatal and intrapartum periods. Digital examination consistently underestimated length by more than 13mm. In contrast, ultrasonographic measurements correlated well with those obtained using a ruler on the postoperative specimen.
      
    Transabdominal ultrasound
    The average cervical length to be between 35-40mm. Up to 6mm dilatation at the internal os was normal with no significant cervical change seen from the 10th to the 36th week of gestation.
     
    115 women with risk factors for cervical incompetence were studied. Patient management was largely based on clinical (as opposed to ultrasound) findings. Of the women with evidence of moderate cervical weakness on ultrasound, one-third were found to have clinically normal cervices. With expectant management, 75% delivered before 34 weeks’ gestation. Most of the remaining two-thirds, underwent cerclage with 25% delivering before 34 weeks.
     
    Riley et al report a 50% risk of preterm birth in women co-incidentally found to have cervical shortening and membrane funneling on transabdominal scanning.
     
    Transvaginal ultrasound:
    Brown et al suggest that adequate cervical images were more likely to be obtained by transvaginal scanning than by transabdominal U.S.G. The cervix could be visualized transvaginally 99% of the time. When transabdominal and transvaginal cervical length measurements from the same woman were compared, transabdominal measurements were on average 5mm longer, presumably secondary to bladder filling. Of the 30 women, 29 demonstrated an increase in cervical length with increasing bladder volume. Confino et al also reported cases in which quantified bladder filling or manual pressure exerted via the transducer led to significant reductions in internal os dilatation in patients with suspected incompetence.
     
    Digital examination only assesses that portion of the cervix below the vaginal wall. Goldberg et al found the mean cervical lengths in 43 pregnant women measured by transvaginal ultrasound (39mm) to be over twice as long as those measured digitally (19mm) by experienced examiners. Similarly, Sonek et al found that digital measurement of cervical length showed a poor correlation with vaginal ultrasonography.
      
    Safety and acceptability:
     
    Heath et al questioned 100 consecutive women about the acceptability of a transvaginal scan at 23 weeks gestation: 94% experienced no, or minimal, discomfort only and 98% reported no or only mild embarrassment. Half of the women found it to be less uncomfortable than a speculum examination.
     
    Normal values for cervical length
    There appears to be no clinically significnat difference between the mean cervical lengths of primiparous and multiparous women.
     
    It is possible that ethnic differences in cervical length exist. The work of National Institute of Child Health and Human Development Maternal-Fetal Medicine Unit Network has shown a short cervix (£ 25mm) to be significantly more common in high risk women.
      
    DIAGNOSTIC ROLE
    Preterm Labour
     
    Murakawa et al studied 32 women presenting with threatened preterm labour. None of the 15 women with cervical lengths greater than 30 mm delivered preterm. If the cervix was less than 30mm, 65% delivered preterm and all early births were identified. All women with a cervical length below 20mm delivered preterm.
     
    Gomez et al developed the term cervical index to include information about endocervical length and funnel length in a single figure. Funneling was present in 58% of women and associated with a nearly 3-fold increase in the risk of preterm birth. A complex statistical analysis suggested that a cervical index ³0.52, cervical length < 18mm, funnel length > 9mm and funnel width > 6mm were all significantly associated with preterm birth. All the patients who delivered preterm had a funnel present.
     
    Cervical anatomy
    The ability to diagnose (or exclude) placenta praevia is one of the main benefits ascribed to antenatal ultrasound. Provided that the placental edge is at least 20mm from the internal os, a vaginal birth appears safe.
     
    Cervical incompetence
    Cervical conization may iatrogenically predispose to cervical incompetence.
     
    Management Role
    Assessment of risk of preterm birth
    Cervical length
     
    3000 women of mixed-risk were screened at both 24 and 28 weeks of gestation. The mean cervical length was approximately 35mm and the overall incidence of spontaneous preterm birth £ 35 weeks’ gestation was 4.3%. There was a clear inverse relationship between cervical length and risk of preterm birth. A short cervix (£ 25mm) was associated with an 8% probability of spontaneous preterm delivery £ 35 weeks gestation in low-risk parous women. In high-risk women, this probability climbed to 31% with the same cervical measurement.
     
    The second study was carried out at a single inner city centre in the UK. Results from cervical scans at 23 weeks’ gestation were blinded unless the length was less than 16mm. A cervical length of £ 15mm at 23 weeks’ gestation carried a risk of spontaneous delivery £ 32 weeks of 50% and correctly identified 58% of these births.
      
    The third study was from a well-defined geographical area in Helsinki, Findland with a 99% white population. The mean cervical length was just over 40mm and a short cervix was defined as one £ 29mm, corresponding to the 3rd centile.
     
    All three studies confirm the ability of transvaginal cervical ultrasound to reliably stratify women by risk of spontaneous preterm birth. Even more importantly, the background or pre-test risk of spontaneous preterm birth must be taken into account when interpreting cervical sonograms.
     
    Membrane funneling
    If the funnel length was greater than the length of closed cervix below it, 75% of patients delivered before 37 weeks’ gestation. A funnel width exceeding 15mm was another risk factor. Heath et al found that all women with a cervical length £ 15mm exhibited funneling compared to only one-third of those with a cervical length of 16-25mm.
     
    Dynamic changes.
    Sonek subsequently reported the same phenomenon in women not believed to have cervical incompetence, using transvaginal scanning. He stated that the funneling could be accentuated or brought on by gentle manual pressure on the uterine fundus and advocated this as an ‘internal os stress test’.
     
    At present, transfundal pressure cannot be standardised. More recently, reports have appeared advocating the use of a postural challenge, with the cervix being scanned first while the mother is supine and then when upright.
     
    Cervical cerclage:
    The final report of the MRC/RCOG Multicentre Randomised Trial of Cervical Cerclage suggested benefit in only 4% of cases with prior clinical uncertainty. Detailed inspection revealed that cerclage improved outcome only after three or more previous very early deliveries. The mean interval between cerclage removal and delivery was 2.3 weeks.
     
    Cerclage placement
    Both Andersen et al and Quinn reported all the McDonald sutures in their series to be in the middle third of the cervix. The optimal placement of a suture was obtained in the single patient that was treated with a Shirodkar-type cerclage, involving preliminary dissection of the anterior vaginal wall.
     
    Post cerclage follow up
    Between 25-30% of patients developed funneling above the cerclage.
     
    Twin pregnancies
    Goldenberg et al scanned 147 twin pregnancies at 24 and 28 weeks’ gestation. A cervical length of less than 25mm was twice as common in twin pregnancies as in singletons and became more common as gestation advanced, occurring in 18% of women at 24 weeks and 33% at 28 weeks.
     
    Cervical ultrasound and routine antenatal care
    Although Zalar suggested that knowledge of transvaginal cervical ultrasound measurements can lead to a reduction in spontaneous low birth-weight deliveries, it cannot yet be concluded that cervical ultrasound has a place in routine antenatal care in low-risk pregnancies.
     
    Preterm prelabour rupture of the membranes
    The authors were unable to demonstrate a significant relationship between cervical length and the number of days to spontaneous labour.
     
    TECHNIQUES FOR CERVICAL SCANNING
    Transabdominal
    Cervical images are best obtained transabdominally with a full bladder. Unfortunately, this is associated with artificial lengthening of the cervix and potential closure of a dilated internal os. Therefore, it will lead to false reassurance in some cases. The external os can also be difficult to identify transabdominally. In the studies of Varma et al, an inflated Foley catheter balloon was placed against it to overcome this problem.
      
    Transvaginal
    This remains the gold standard for cervical imaging. Sonek et al have advocated the use of a probe with a 240° scanning field, this would appear to be unnecessary. Pressure on the cervix can falsely increase the measured length and obscure funneling at the internal os. Failing to appreciate that not all cervical canals follow a straight line can lead to underestimates of length. At least 3 measurements should be taken and the shortest (not the average) used. Most authors advise scanning over approximately 5 min to detect dynamic changes. The presence of a funnel should be noted and funnel width and length recorded. Some authors have reserved the term ‘funnel’ for membrane protrusions greater than 5mm down the endocervical canal, referring to anything less as ‘nippling’.
     
    Transperineal scanning
    A glove-covered 3.5MHz or 5 MHz sector or curvilinear transducer is applied to the perineum to visualize the cervix. It is reportedly easily tolerated by patients, but is best performed before digital or speculum examination which, by introducing air into the vagina, produce artefact. The technique has been particularly useful in cases of prolapsing membranes when cerclage is not being undertaken. The contrast provided by the funnel or membranes usually allows excellent visualization and serial monitoring. Transperineal ultrasonography may prove to be an acceptable mass screening technique.
     
    CONCLUSIONS:
     
    As proposed by Iams et al, ultrasound imaging suggests cervical competence to be a continuous variable. Infection has attracted considerable interest as one of the most important aetiologies behind preterm labour and delivery. A weak or short cervix could offer less resistance to ascending infection. Half have positive amniotic fluid cultures. 
     
    Iams et al have recently reported that a cervical length of less than 25mm at 24 weeks’ gestation is strongly associated with subsequent perinatal infection. Bacteria can ascend the genital tract attached to motile sperm. Antibiotics may play just as important a role as cervical cerclage in preventing prematurity. As prostaglandins are implicated in the process of cervical ripening, non-steroidal anti-inflammatories such as indomethacin may have role for ultrasonographic cervical change, at least before 28 weeks’ gestation. Cervical ultrasound undoubtedly allows a far better assessment of risk than clinical examination.
     

  • Frank Johnstone (Department of Obstetrics and Gynaecology, University of Edinburgh UK)
    Drug Use in Pregnancy
    Progress in Obstetric and Gynaecology vol.14
     
    This article is about a broad range of drugs which have some psycho-active properties and which are used for non-therapeutic reasons in pregnancy.
     
    All the drugs (with the possible exception of benzodiazepines) appear to have a common final pathway. They all act by increasing dopamine release. But for all of them, the common end-point where dopamine is released forms part of a circuit known as the brain reward system, consisting of a small group of nerve cells extending from the ventral tegmental area of the midbrain to limbic areas such as the nucleus accumbens, with projections to the pre-frontal cortex. The markedly reduced activity in the brain reward circuits on withdrawal also explains dependence.
     
    Over the past few decades, use has spread to most countries of the world. This is due partly to a general increase in use of psycho-active drugs, improvements in communication and transportation and the globalisation of the world economy. Indeed, tobacco companies have used international trade agreements to open up markets in the developing world, and the same factors facilitating trade in legal goods also facilitate trade in illicit drugs.
     
    Many women, who do not acknowledge any problem with their drug pattern, may present for the first time to the health care system because of the pregnancy. This presents a window of opportunity for harm minimisation and education. Pregnancy can be a great motivator. Drug use in pregnancy is already known to be a major public health problem.
     
    Some Effects of Drugs on Pregnancy
    Effects in animal studies (often with high doses) may be due to maternal toxicity rather than direct effects on the fetus (e.g. drug induced anorexia). There may be selection bias based on obvious chaotic drug use, so that the women studies are quite unrepresentative of population use. The small numbers studied may be inadequate to study infrequent events. Because of editorial and reviewer bias there may be preferential publication of studies which report harmful effects. Many drug users are polydrug users and this makes it difficult to isolate the effect of one drug. There are major problems in separating the effects of drug use from the other adverse personal, psychological and social circumstances in which drug use is taking place.
     
    Opioids
    Injecting street heroin is dangerous and in most cohorts of users the mortality is at least 1% each year. The commonest cause of death is respiratory depression due to overdose. The other major medical complications relate largely to non-sterile injecting, resulting in transmission of hepatitis B, and most importantly hepatitis C and HIV.
     
    There is no convincing evidence that opioids cause fetal abnormalities.They probably have a small inhibiting effect on fetal growth, though this is less than the effects of smoking. In all large studies, there is a modest increase in perinatal mortality due to preterm delivery and late pregnancy stillbirth, but it is uncertain how much of this drug is a drug effect rather than due to the effect of other variables. Preterm labour does seem to be more common in women injecting drugs rather than taking orally, possibly related to a higher risk of alternation between intoxication and withdrawal with relatively short acting injected drugs. An increase in meconium staining of the liquor is also consistently reported, related to episodes of fetal drug withdrawal.
     
    There is a high rate of neonatal abstinence syndrome (NAS), ranging from 50-90% in women taking opiates daily. Symptoms may last for weeks or even months in a mild form. Typically, babies feed poorly and have tremor on handling, a shrill cry, sneeze and may have watery stools. Untreated, they can develop projectile vomiting and electrolyte disturbance, seizures and coma. 
     
    The largest study of 1760 cases of sudden infant death syndrome, showed a 7 times increased risk with maternal methadone use and a 5 times increased risk with heroin use. 
     
    Drug effects, and the consequences of an unstable, impoverished environment, are very difficult to disentangle, but this remains an area of concern.
     
    Cocaine.
    As well as its central action, this drug has important peripheral effects on inhibition of re-uptake of noradrenaline in presynaptic nerve terminals. Catecholamines diffuse from the nerve terminals and the resulting high vascular levels cause vasoconstriction, tachycardia, hypertension and perhaps uterine contractility.
     
    The vasoconstrictive properties of cocaine raise the possibility that there might be fetal damage during episodes of fetal ischaemia or subsequent reperfusion. However, the overall population risk for users does not seem very high, perhaps because only those with high dosage at key gestations are vulnerable. A large number of studies in women are consistent in reporting a decrease in birth weight. Preterm delivery is common and, although it is very difficult to adjust for multiple co-variates this is probably also a direct drug effect.
     
    Nicotine
    Of the 4000 compounds in tobacco smoke, there is good evidence that nicotine is the key drug of addiction and nicotine, carbon monoxide and cyanide are thought to have the greatest adverse effect on the fetus. World-wide, this is the most harmful drug for pregnancy.
     
    There are well documented increased risks of spontaneous abortion, ectopic pregnancy, placenta praevia, placental abruption, preterm premature rupture of the membranes and preterm delivery. Birth weight is depressed by about 250g, with an increased risk of significant intra-uterine growth restriction. Intrauterine death in late pregnancy is more common. Overall, at least in the US, smoking causes an estimated 20-30% of the low birth weight rate and 10% of fetal and infant mortality. Postnatally, maternal milk production is reduced by about 30%. There are strong relationships with sudden infant death syndrome; respiratory disease and hospital admission in the first year of life; and an ongoing effect on respiratory disease in childhood. There are small effects on physical, mental and behavioural development of the child, of uncertain clinical significance.
     
    There may be other long-term complications. Potentially carcinogenic tobacco metabolites are present in the first urine of babies whose mothers smoked in pregnancy. The babies of women who smoke were found to have a much higher frequency of a genomic deletion event that is commonly found in leukaemia and lymphomas of early childhood.
     
    Benzodiazepines
    Diazepam overdose in 25 pregnancies was not accompanied by obvious fetal problems. Withdrawal may occur in the neonate, typically with irritability and slowness to feed and respond. There may be ‘floppy infant syndrome’ with poor suck, feeble cry, hypotonia, and sometimes poor temperature control.
     
    Cannabis
    Most studies have not reported an association between prenatal marijuana exposure and morphological abnormalities of the baby.
     
    Amphetamines
    Data currently available do not allow any accurate estimate of risk.
     
    Designer drugs
    The most widely used drugs at present are amphetamine analogues. Ecstasy (3,4 methylenedioxymethyl amphetamine, MDMA) is one derivative related chemically to both amphetamines and hallucinogens.
     
    Alcohol
    This is the only one of these drugs which is proven to be teratogenic. Fetal alcohol syndrome (FAS) has been reviewed in a previous issue of this series. A wide range of other alcohol-related birth defects appear to occur with heavy drinking. These adverse effects have been well documented with very high maternal intakes. Judging by animal experiments, alcohol may affect fetal brain development at any gestation. Threshold effects on subsequent reading, spelling and arithmetic abilities in children have been reported at low intakes.
     
    Volatile substances
    The commonest substance is cigarette lighter refills (butane) but a wide range of products are used.
      
    OPTIONS FOR DRUG MANAGEMENT
    Many women who are not truly dependent on their drug will stop spontaneously as soon as they know they are pregnant. This applies to 15-20% of women who smoke, to many women who use ecstasy or cannabis episodically and it is also true of some controlled users of opiates.
     
    It is said that most girls who smoke 3 cigarettes as adolescents will become dependent, with an average duration of dependence of 40 years. Sadly, having been recruited in adolescence, half of all smokers die because of the habit, one-third of them before the age of 65 years. 20% of all deaths in developed countries are caused by smoking: an enormous human cost which can be completely avoided.
     
    Therefore, antenatal care should include advice to stop smoking, with easy access to programmes to support those who choose this. Brief intervention by family doctors is effective. Cutting down is probably not a useful aim. 
     
    Trying to persuade the woman to stop drugs may simply alienate her, lead to return to a more chaotic drug use pattern, and result in non-attendance for antenatal care. Therefore, the different options of detoxification, substitution and maintenance and other aspects of damage limitation need to be considered with full understanding of the woman’s aspirations and particular social and psychological circumstances.
     
    For most women who are dependent and who have a long-standing opiate habit, substitution and maintenance is usually the preferred option. The drug of choice is methadone linctus. Methadone maintenance treatment has been extensively researched, and has been shown to be effective. Substitution should be prescribed as part of a package including social and psychological support.
     
    Acute detoxification in pregnancy is not often appropriate but should be an option. The risks of withdrawal have probably been exaggerated in the past, and can be minimised by appropriate drug therapy to the mother. Detoxification can be carried out in the mid-trimester quite safely and this has a place in overall management.
     
    Slow reduction may be preferred by some women for opiates, and is necessary for benzodiazepines.
     
    Much of the management of drug misuse is damage limitation rather than cure, and in patients who continue to inject, it is essential to ensure that they have access to clean equipment, by needle exchange.
       
    Maternity Care in Drug Users
    Another important obligation on community care staff is effective liaison and communication with other agencies. Nothing is so guaranteed to reduce confidence as different agencies giving out different messages.
        
    The opiate using woman should be warned that neonatal abstinence syndrome may occur, that her dose is not a reliable predictor, that it can present after several days and can last for weeks. She needs also to know that NAS is usually easily manageable.
       
    Repeated non-sterile injection over years destroys peripheral veins, often leaving track marks (thrombosed, fibrosed veins). Occasionally there may be concern about the ability of the woman to look after her child. Many women worry that their baby may be taken away into care purely because they use drugs.
       
    Occasionally, there maybe incidents involving violence or the threat of violence, most often caused by the partner or visiting friends in hospital.
       
    Adequate pain relief can be obtained with opiates although much more frequent injections are likely to be needed. Because of the high fear about pain which many drug users have, epidural anaesthesia may be very useful.
        
    Naloxone must not be used to reverse opioid induced respiratory depression in the newborn because of the risk of precipitating an acute opiate withdrawal crisis.
        
    After delivery, a chart scoring for neonatal abstinence syndrome is helpful for all concerned. This is, of course, only one aspect of assessment. Withdrawing babies can usually be treated without drug management, with lots of cuddling, small frequent feeds, and patience. Babies may need neonatal unit care to maintain hydration and may need sedation. The logical drug is simply replacement of opiate, and neonatal morphine solution can be used.
          

  • Alessandro Ghidini, Nicola Strobelt, Anna Locatelli, Eloisa Mariani, Maria Giovanna Piccoli, and Patrizia Vergani
    Isolated Fetal Choroid Plexus Cysts : Role of Ultrasonography in Establishment of the Risk of Trisomy 18
    Am J. Obstet Gynecol April 2000, Volume 182, Number 4, Pgs. 972-977
        
    Objective – The significance of isolated choroid plexus cysts found by ultrasonographic scan during the second trimester as a marker for trisomy 18 is 
    still debated. We analyzed our data and reviewed the series published in the English-language literature to calculate the likelihood ratio of trisomy 18 in the presence of isolated choroid plexus cysts; that is, the factor by which the individual risk of trisomy 18 is increased in the presence of isolated choroid plexus cysts.
        
    Study Design – Likelihood ratios were calculated as ratio of the sensitivity to the faise-positive rate. Sensitivity was defined as the rate of isolated choroid plexus cysts detected at midgestation among fetuses with trisomy 18. False-positive rate was defined as the rate of choroid plexus cysts detected at midgestation in the population without trisomy 18. The sensitivities of all published series reporting rates of choroid plexus with trisomy 18 and in low-risk populations were included in the analysis. To these we added all cases of trisomy 18 diagnosed at our institution during the period January 1, 1988, through June 30, 1998, in which prenatal ultrasonographic examination was performed between 14 and 24 weeks’ gestation. 
       
    Results – The prevalence of second-trimester ultrasonographic detection of isolated choroid plexus cysts among fetuses with trisomy 18 was 6.7% [ 13/194]. Whereas that in the population without trisomy 18 was 0.9% [752/79, 583]. The likelihood ratio associated with isolated choroid plexus cysts was therefore 7.09 [95% confidence interval, 3.97 -12.18]
       
    Conclusion – The presence of isolated second-trimester choroid plexus cysts increases the base risk of trisomy 18 by a factor of 7.09. This likelihood ratio can be multiplied by the risk calculated according to maternal age to obtain the individual risk of trisomy 18 and thus permit more accurate counseling of the patient.
        

  • Karim D. Kalache, Roland Wauer, Harald Mau, Rabih Chaoui, and Rainer Bollmann
    Prognostic Significance of the Pouch Sign in Fetuses with Prenatally Diagnosed Esophageal Atresia
    Am J. Obstet Gynecol April 2000, Volume 182, Number 4, Pgs. 978-981
       
    Objective – Esophageal atresia may be diagnosed prenatally by ultrasonographic visualization of the blind-ending esophagus during fetal swallowing, which is referred to as the pouch sign. Our purpose was to determine whether this sign can be used to predict outcomes of affected fetuses. 
       
    Study Design – Four cases of esophageal atresia diagnosed in our center during the past 2 years were analyzed, in conjunction with 3 cases from published series. Ultrasonographic features of the pouch sign were categorized according to localization.
       
    Results – In the neck pouch group [ n=3] 1 fetus died in utero and 1 died before a corrective operation could be undertaken. In the only fetus of this group to survive a staged repair was necessary because of a long atretic gap. Conversely, 3 of the 4 fetuses with a mediastinal pouch survived after a successful corrective operation, and primary repair was possible in all cases.
       
    Conclusions – The base of the proximal blind-ending esophagus can be clearly localized by means of ultrasonography. Our data suggest that a neck pouch may be associated with an adverse outcome. This information may be useful in counseling parents when esphageal atresia is diagnosed prenatally.
         

      

 

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