Speciality
Spotlight

 




 


Obstetric & Gynaecology


 

 




Fetal
Anomalies in the First Trimester

         

  • Whitlow
    B.J., Economides D.L 


    Screening for fetal anomalies in the first
    trimester.


    Progress in Obstetric &Gynaecology 14th
    vol.,edited by John Studd.

     


    One child in 55 will be born with a major structural
    abnormality. Such abnormalities can contribute up to
    15% of perinatal deaths and a similar number of
    deaths in the first year of life. The most common
    reasons for terminating a fetus with a serious
    anomaly are neural tube defects followed by
    chromosome abnormality.

     


    It is not just for terminating that prenatal
    diagnosis is useful. It has profound implications on
    antenatal and intrapartum management. Certain
    malformations can be treated in utero (e.g.
    diaphragmatic hernia) or postnatally (e.g. certain
    cardiac defects), so early diagnosis can facilitate
    decision making regarding mode and place of
    delivery, especially if neonatal resuscitation and
    immediate surgery are required.

     


    The Royal College of Obstetricians and
    Gynaecologists recommend an ultrasound examination
    at 18-20 weeks. Should fetal abnormalities be
    detected at this stage, a second trimester
    termination may be necessary and this is associated
    with marked psychological sequelae in around 25% of
    cases. It is assumed that if prenatal diagnosis is
    made earlier then a safer first trimester
    termination could be achieved.

     


    GENERAL USES OF SONOGRAPHY IN THE FIRST TRIMESTER

     


    It is important to accurately date a woman’s
    pregnancy. It is possible to accurately predict
    gestational age to within 7 days in the first
    trimester. Viability of a pregnancy can also be
    determined when the crown-rump length is 6mm or more
    and/or the mean gestational sack diameter is 20mm or
    more. If there is absence of cardiac activity in the
    presence of the aforementioned criteria, then the
    pregnancy can be diagnosed as being non-viable.
    Determination of chorionicity in multiple
    pregnancies can be more easily detected in the first
    trimester, as the lambda sign (suggesting
    dichorionicity) becomes obliterated at later
    gestations. Early ultrasound may re-assure those
    mothers with increased anxiety (especially those who
    have had a previous ectopic pregnancy or those that
    suffer from recurrent early miscarriages). Indeed
    the presence of a viable fetus at 12-13 weeks’
    gestation may be associated with a live birth in
    over 98% of cases.

     


    A significant proportion i.e.2.2% of pregnancies at
    11-14 weeks will have failed and the detection of
    such missed abortions will enable a planned
    evacuation of the uterus. The anomalies can be
    structural or chromosomal. The problem of diagnosing
    structural anomalies early is that pathological
    confirmation is technically more difficult, time
    consuming and impossible if suction termination is
    performed.

     


    Feasibility of examining fetal anatomy in the first
    trimester.

    Feasibility of TAS.

     


    Green and Hobbins observed that detailed fetal
    anatomy could be visualized with TAS in the first
    trimester.

     


    Advantages of TAS

    Probe manoeuvrability is superior with
    transabdominal sonography (TAS).

     


    Advantages of TVS

    TVS in general has superior resolution over TAS.
    Bladder filling for TAS was found to cause marked
    discomfort in 4.9%, whilst marked discomfort with
    TVS was found in only 0.7%. 

     


    TAS versus TVS

    Cullen concluded that TVS was better used to
    complete, not replace TAS examination for the
    visualization of the first trimester fetus. 

     


    TVS, however, took longer than TAS, with the mean
    scan time for a complete anatomical survey being
    11min for TAS and 16 min for TVS. Complete
    anatomical surveys were performed in 72% by TAS and
    82% by TAS, and in 95% using a combination of both
    scan modes.

     


    The unique appearance of fetal organs in the first
    trimester.

     


    The choroid plexi completely fill the lateral
    borders of the posterior and anterior ventricles,
    and this in turn occupies most of the hemisphere;
    thus hydrocephalus can be potentially difficult to
    diagnose in the first trimester. So also with
    anencephaly, a ‘Mickey Mouse’ appearance, is seen
    which is different from ‘frogs’ eye in the second
    trimester. An omphalocele should not be considered
    as abnormal unless the crown-rump length of the
    fetus is ³ 46mm, since the bowel is present in the
    umbilical cord in early embryonic development.

     


    The heart is difficult to visualize in detail in the
    first trimester. Dolkar et al assessed the 4
    chambers view including the major outlet vessels and
    found that by 12 weeks some 90%, and 13 weeks 100%,
    of cardiac views were satisfactory. The kidneys’
    appearance changes with gestation, being very
    echodense at 9-10 weeks and becoming more sonolucent
    at 11 weeks as excretory function begins.

     


    Since excretory function only occurs after 11 weeks,
    major renal tract anomalies are unlikely to be
    visualized before this time. The hands are often
    open in the first trimester, thus making it easier
    to count the digits and examine for polydactyly.

      


    NUCHAL TRANSLUCENCY MEASUREMENT

     


    Nuchal oedema, or nuchal translucency (NT) as it is
    now more commonly known, is measured from a sagittal
    view of the fetus and is the maximum thickness of
    subcutaneous translucency between the skin and soft
    tissues overlying the cervical spine.

     


    A sonographer is considered trained to measure NT,
    and this is usually achieved after 80-100 supervised
    scans.

     


    Standardising nuchal translucency measurement.

     


    Position

    Most studies examining NT in the first trimester
    will measure the NT in the midline sagittal plane
    and measure only the sonolucent (black) area between
    the fetal spine and skin at 28-83 mm crown-rump
    length. A NT will be different when the fetal neck
    is in neutral positions, flexed, or extended. They
    found that fetal umbilical cord can be positioned
    around the neck in 8.23% of fetuses at 10-14 weeks’
    gestation, and that this can add a mean of 0.8mm to
    the NT measurement.

     


    Charts were constructed to derive the probabilities
    of a fetus being affected by a chromosomal
    abnormality on the basis of maternal age combined
    with NT mesurement. Using this method, an 85%
    sensitivity for the detection of fetal chromosomal
    abnormality was predicted with a false positive rate
    of 5%. Investigators have since found that
    measurement of NT, increases with gestation to a
    peak at 13 weeks, after which it decreases.
    Consequently, the use of a single NT threshold value
    for all gestations (10-14 weeks) is incorrect.

     


    Nuchal translucency in unselected populations

     


    Without taking maternal age into consideration and
    using either the 99th centile for nuchal
    translucency or the presence of a structural
    abnormality as indications for karyotyping, were
    able to diagnose 18% of chromosomal abnormalities
    and 75% of cases of trisomy 21 at 11-14 weeks.

     


    This is the largest UK multicentre trial (96,127
    women) involving NT to date. They found that on
    average 30 invasive tests would be required to
    identify one affected fetus.

     


    Sonographic markers for chromosomal abnormalities in
    the first trimester.

     


    The significance of ‘soft’ ultrasound markers for
    the detection of chromosomal abnormalities in the
    first trimester is unknown. Fetuses with markers in
    the first trimester were not necessarily the same
    fetuses with markers in the second trimester. The
    presence of two or more such markers should
    stimulate the clinician to discuss invasive
    karyotyping with the patient in the first trimester.

     


    Outcome of fetuses with enlarged nuchal translucency
    and a normal karyotype.

     


    Souka et al in a study of over 4000 such cases,
    found that a live birth can be expected in 94.4%.
    Structural abnormalities can be expected in 10-17%
    of cases. Equally, genetic syndromes and single gene
    disorders can be expected in an additional 12% of
    fetuses. Thus the chances of taking home a normal
    baby in the presence of an increased NT is around
    34% (when chromosomal structural, genetic syndromes
    and miscarraiges are considered together).

     


    Nuchal translucency and cardiac abnormalities.

     


    Increased NT is also associated with cardiac system
    abnormalities; the greater the measurement of NT,
    the more severe the abnormality. Karyotypically
    normal fetuses with increased NT should have
    mid-trimester fetal echocardiography

     


    The benefits of first-trimester sonography for the
    detection of Down’s syndrome depend on its
    diagnostic accuracy, but it has the potential for
    annual savings of $22 million in the US.

     


    Maternal first trimester serum biochemical screening

     


    Wald et al measured free b-hCG and PAPP-A at 18-14
    weeks’ gestation and found that the respective
    multiple of the median values in those pregnancies
    affected by Down’s syndrome were on average 1.79 and
    0.43, respectively. The combination of these two
    markers were shown to be 63% sensitive and 94.5%
    specific. Other markers are not found to be useful.

     


    Nuchal translucency and first trimerster biochemical
    markers.

     


    It was reported that Down’s syndrome was detected by
    biochemistry in 61%, by nuchal translucency in 73%
    and in 87% by combining both methods for a 5%
    false-positive rate. Future maternal biochemical
    screening may invovle blood being taken at initial
    ultrasound visit (11-14 weeks) and results being
    available by the end of the scan, thus improving
    efficiency and giving the mother one single risk
    figure. 

     


    The optimal gestational age to perform the first
    trimester scan

     


    It was found that the optimal gestational age to
    examine fetal anatomy and measure nuchal
    translucency in the first trimester to be at 13
    weeks.

     


    Fetal trimester detection of fetal structural
    abnormalities

     


    It was found that performing the first ultrasound at
    a later gestational age would miss transient
    anomalies associated with chromosomally abnormal
    fetuses, and suggested that screening in the early
    mid-trimester be offered to everyone.

     


    Screening low-risk populations for structural
    anomalies

     


    A total of 5,616 patients have been studied so far.
    The abnormality rate was found to be 0.8% (47/5616).
    Thirty-two of these abnormalities were diagnosed in
    the first trimester (685 sensitivity), with a
    specificity of 99.9%.

     


    Fetal abnormalities from all the major systems have
    been diagnosed in the first trimester. Certain
    abnormalities are more easily detectable at 11-14
    weeks than others. First trimester sonography was
    found to be particularly good for diagnosing central
    nervous system defects, neck anomalies,
    gastrointestinal and renal defects. A lemon shaped
    skull in the first trimester has been described and
    this may prove to aid diagnosis of spina-bifida. The
    detection of cardiac abnormalities in the first
    trimester in this study was below what one might
    expect when compared to the second trimester scan
    i.e.38% vs 69%.

     


    Some 17% of abnormalities not detected at 13-16
    weeks were subsequently detected at the 18-20 week
    scan. The anomalies not diagnosed by the combination
    of first and second trimester scans are mainly heart
    and limb defects. Thus, in karyotypically normal
    fetuses with increased NT, there maybe a place for
    mid-trimester fetal echocardiography at 22-24 weeks’
    gestation when the cardiovascular system can be
    better visualised. 

     


    Some abnormalities, however, develop as a transitory
    finding in the first trimester and may not be
    present at later gestations (e.g. cystic hygromas
    and nuchal translucency). Thus the sonographer
    should be aware of the chronological order of
    development of specific malformations. Therefore, a
    single scan in pregnancy will not detect all fetal
    malformations.

     


    Thus, in the second trimester scan, there should be
    more emphasis on diagnosing the more difficult
    anomalies by concentrating on the heart, spine and
    limbs.

     


    The main reason for this physiological bowel
    herniation in to the cord that does occur up to 11
    weeks and can be mistaken for exomphalos.

     


    The psychological aspects first trimester scanning.

     


    It has been shown that the level of psychological
    morbidity following termination for fetal
    abnormality in the second trimester is similar to
    that following spontaneous perinatal loss and is of
    the order of 25%.

     


    Finanical implications of screening for fetal
    anomalies in the first trimester.

      


    They found that first trimester sonography at 11-14
    weeks could detect the majority of fetal structural
    defects (68%) and chromosomal defects (79%), at an
    estimated cost per abnormality of Pound 6885 for
    detecting fetal aneuploidy, Pound 5809 per case for
    structural defects and Pound 3955 per anomalous
    fetus.

     



    CONCLUSIONS:


    Nuchal translucency screening for Down’s syndrome
    has been given a grade B recommendation by the RCOG
    working party, as has serum screening at 9-13 weeks.

     

 

      



 

 

Speciality Spotlight

 

 

Fetal Anomalies in the First Trimester
         

  • Whitlow B.J., Economides D.L 
    Screening for fetal anomalies in the first trimester.
    Progress in Obstetric &Gynaecology 14th vol.,edited by John Studd.
     
    One child in 55 will be born with a major structural abnormality. Such abnormalities can contribute up to 15% of perinatal deaths and a similar number of deaths in the first year of life. The most common reasons for terminating a fetus with a serious anomaly are neural tube defects followed by chromosome abnormality.
     
    It is not just for terminating that prenatal diagnosis is useful. It has profound implications on antenatal and intrapartum management. Certain malformations can be treated in utero (e.g. diaphragmatic hernia) or postnatally (e.g. certain cardiac defects), so early diagnosis can facilitate decision making regarding mode and place of delivery, especially if neonatal resuscitation and immediate surgery are required.
     
    The Royal College of Obstetricians and Gynaecologists recommend an ultrasound examination at 18-20 weeks. Should fetal abnormalities be detected at this stage, a second trimester termination may be necessary and this is associated with marked psychological sequelae in around 25% of cases. It is assumed that if prenatal diagnosis is made earlier then a safer first trimester termination could be achieved.
     
    GENERAL USES OF SONOGRAPHY IN THE FIRST TRIMESTER
     
    It is important to accurately date a woman’s pregnancy. It is possible to accurately predict gestational age to within 7 days in the first trimester. Viability of a pregnancy can also be determined when the crown-rump length is 6mm or more and/or the mean gestational sack diameter is 20mm or more. If there is absence of cardiac activity in the presence of the aforementioned criteria, then the pregnancy can be diagnosed as being non-viable. Determination of chorionicity in multiple pregnancies can be more easily detected in the first trimester, as the lambda sign (suggesting dichorionicity) becomes obliterated at later gestations. Early ultrasound may re-assure those mothers with increased anxiety (especially those who have had a previous ectopic pregnancy or those that suffer from recurrent early miscarriages). Indeed the presence of a viable fetus at 12-13 weeks’ gestation may be associated with a live birth in over 98% of cases.
     
    A significant proportion i.e.2.2% of pregnancies at 11-14 weeks will have failed and the detection of such missed abortions will enable a planned evacuation of the uterus. The anomalies can be structural or chromosomal. The problem of diagnosing structural anomalies early is that pathological confirmation is technically more difficult, time consuming and impossible if suction termination is performed.
     
    Feasibility of examining fetal anatomy in the first trimester.
    Feasibility of TAS.
     
    Green and Hobbins observed that detailed fetal anatomy could be visualized with TAS in the first trimester.
     
    Advantages of TAS
    Probe manoeuvrability is superior with transabdominal sonography (TAS).
     
    Advantages of TVS
    TVS in general has superior resolution over TAS. Bladder filling for TAS was found to cause marked discomfort in 4.9%, whilst marked discomfort with TVS was found in only 0.7%. 
     
    TAS versus TVS
    Cullen concluded that TVS was better used to complete, not replace TAS examination for the visualization of the first trimester fetus. 
     
    TVS, however, took longer than TAS, with the mean scan time for a complete anatomical survey being 11min for TAS and 16 min for TVS. Complete anatomical surveys were performed in 72% by TAS and 82% by TAS, and in 95% using a combination of both scan modes.
     
    The unique appearance of fetal organs in the first trimester.
     
    The choroid plexi completely fill the lateral borders of the posterior and anterior ventricles, and this in turn occupies most of the hemisphere; thus hydrocephalus can be potentially difficult to diagnose in the first trimester. So also with anencephaly, a ‘Mickey Mouse’ appearance, is seen which is different from ‘frogs’ eye in the second trimester. An omphalocele should not be considered as abnormal unless the crown-rump length of the fetus is ³ 46mm, since the bowel is present in the umbilical cord in early embryonic development.
     
    The heart is difficult to visualize in detail in the first trimester. Dolkar et al assessed the 4 chambers view including the major outlet vessels and found that by 12 weeks some 90%, and 13 weeks 100%, of cardiac views were satisfactory. The kidneys’ appearance changes with gestation, being very echodense at 9-10 weeks and becoming more sonolucent at 11 weeks as excretory function begins.
     
    Since excretory function only occurs after 11 weeks, major renal tract anomalies are unlikely to be visualized before this time. The hands are often open in the first trimester, thus making it easier to count the digits and examine for polydactyly.
      
    NUCHAL TRANSLUCENCY MEASUREMENT
     
    Nuchal oedema, or nuchal translucency (NT) as it is now more commonly known, is measured from a sagittal view of the fetus and is the maximum thickness of subcutaneous translucency between the skin and soft tissues overlying the cervical spine.
     
    A sonographer is considered trained to measure NT, and this is usually achieved after 80-100 supervised scans.
     
    Standardising nuchal translucency measurement.
     
    Position
    Most studies examining NT in the first trimester will measure the NT in the midline sagittal plane and measure only the sonolucent (black) area between the fetal spine and skin at 28-83 mm crown-rump length. A NT will be different when the fetal neck is in neutral positions, flexed, or extended. They found that fetal umbilical cord can be positioned around the neck in 8.23% of fetuses at 10-14 weeks’ gestation, and that this can add a mean of 0.8mm to the NT measurement.
     
    Charts were constructed to derive the probabilities of a fetus being affected by a chromosomal abnormality on the basis of maternal age combined with NT mesurement. Using this method, an 85% sensitivity for the detection of fetal chromosomal abnormality was predicted with a false positive rate of 5%. Investigators have since found that measurement of NT, increases with gestation to a peak at 13 weeks, after which it decreases. Consequently, the use of a single NT threshold value for all gestations (10-14 weeks) is incorrect.
     
    Nuchal translucency in unselected populations
     
    Without taking maternal age into consideration and using either the 99th centile for nuchal translucency or the presence of a structural abnormality as indications for karyotyping, were able to diagnose 18% of chromosomal abnormalities and 75% of cases of trisomy 21 at 11-14 weeks.
     
    This is the largest UK multicentre trial (96,127 women) involving NT to date. They found that on average 30 invasive tests would be required to identify one affected fetus.
     
    Sonographic markers for chromosomal abnormalities in the first trimester.
     
    The significance of ‘soft’ ultrasound markers for the detection of chromosomal abnormalities in the first trimester is unknown. Fetuses with markers in the first trimester were not necessarily the same fetuses with markers in the second trimester. The presence of two or more such markers should stimulate the clinician to discuss invasive karyotyping with the patient in the first trimester.
     
    Outcome of fetuses with enlarged nuchal translucency and a normal karyotype.
     
    Souka et al in a study of over 4000 such cases, found that a live birth can be expected in 94.4%. Structural abnormalities can be expected in 10-17% of cases. Equally, genetic syndromes and single gene disorders can be expected in an additional 12% of fetuses. Thus the chances of taking home a normal baby in the presence of an increased NT is around 34% (when chromosomal structural, genetic syndromes and miscarraiges are considered together).
     
    Nuchal translucency and cardiac abnormalities.
     
    Increased NT is also associated with cardiac system abnormalities; the greater the measurement of NT, the more severe the abnormality. Karyotypically normal fetuses with increased NT should have mid-trimester fetal echocardiography
     
    The benefits of first-trimester sonography for the detection of Down’s syndrome depend on its diagnostic accuracy, but it has the potential for annual savings of $22 million in the US.
     
    Maternal first trimester serum biochemical screening
     
    Wald et al measured free b-hCG and PAPP-A at 18-14 weeks’ gestation and found that the respective multiple of the median values in those pregnancies affected by Down’s syndrome were on average 1.79 and 0.43, respectively. The combination of these two markers were shown to be 63% sensitive and 94.5% specific. Other markers are not found to be useful.
     
    Nuchal translucency and first trimerster biochemical markers.
     
    It was reported that Down’s syndrome was detected by biochemistry in 61%, by nuchal translucency in 73% and in 87% by combining both methods for a 5% false-positive rate. Future maternal biochemical screening may invovle blood being taken at initial ultrasound visit (11-14 weeks) and results being available by the end of the scan, thus improving efficiency and giving the mother one single risk figure. 
     
    The optimal gestational age to perform the first trimester scan
     
    It was found that the optimal gestational age to examine fetal anatomy and measure nuchal translucency in the first trimester to be at 13 weeks.
     
    Fetal trimester detection of fetal structural abnormalities
     
    It was found that performing the first ultrasound at a later gestational age would miss transient anomalies associated with chromosomally abnormal fetuses, and suggested that screening in the early mid-trimester be offered to everyone.
     
    Screening low-risk populations for structural anomalies
     
    A total of 5,616 patients have been studied so far. The abnormality rate was found to be 0.8% (47/5616). Thirty-two of these abnormalities were diagnosed in the first trimester (685 sensitivity), with a specificity of 99.9%.
     
    Fetal abnormalities from all the major systems have been diagnosed in the first trimester. Certain abnormalities are more easily detectable at 11-14 weeks than others. First trimester sonography was found to be particularly good for diagnosing central nervous system defects, neck anomalies, gastrointestinal and renal defects. A lemon shaped skull in the first trimester has been described and this may prove to aid diagnosis of spina-bifida. The detection of cardiac abnormalities in the first trimester in this study was below what one might expect when compared to the second trimester scan i.e.38% vs 69%.
     
    Some 17% of abnormalities not detected at 13-16 weeks were subsequently detected at the 18-20 week scan. The anomalies not diagnosed by the combination of first and second trimester scans are mainly heart and limb defects. Thus, in karyotypically normal fetuses with increased NT, there maybe a place for mid-trimester fetal echocardiography at 22-24 weeks’ gestation when the cardiovascular system can be better visualised. 
     
    Some abnormalities, however, develop as a transitory finding in the first trimester and may not be present at later gestations (e.g. cystic hygromas and nuchal translucency). Thus the sonographer should be aware of the chronological order of development of specific malformations. Therefore, a single scan in pregnancy will not detect all fetal malformations.
     
    Thus, in the second trimester scan, there should be more emphasis on diagnosing the more difficult anomalies by concentrating on the heart, spine and limbs.
     
    The main reason for this physiological bowel herniation in to the cord that does occur up to 11 weeks and can be mistaken for exomphalos.
     
    The psychological aspects first trimester scanning.
     
    It has been shown that the level of psychological morbidity following termination for fetal abnormality in the second trimester is similar to that following spontaneous perinatal loss and is of the order of 25%.
     
    Finanical implications of screening for fetal anomalies in the first trimester.
      
    They found that first trimester sonography at 11-14 weeks could detect the majority of fetal structural defects (68%) and chromosomal defects (79%), at an estimated cost per abnormality of Pound 6885 for detecting fetal aneuploidy, Pound 5809 per case for structural defects and Pound 3955 per anomalous fetus.
     
    CONCLUSIONS:
    Nuchal translucency screening for Down’s syndrome has been given a grade B recommendation by the RCOG working party, as has serum screening at 9-13 weeks.
     

 

      

 

By |2022-07-20T16:43:10+00:00July 20, 2022|Uncategorized|Comments Off on Fetal Anomalies in the First Trimester

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