Speciality
Spotlight

 




 

Obstetric & Gynaecology

 

 




Preterm Labour



   

  • TO Scholl (Univ of Medicine and Dentistry of New Jersey, Stratford

    High third trimester ferritin concentration: Associations with very preterm delivery, infection, and maternal nutritional status.) 

    Obstet Gynecol, 92:161-166, 1998.

        


    Very preterm delivery is caused by sub clinical maternal infections. Prospective follow up study included 1162 gravidas with a high serum ferritin levels at week 28.

        


    High serum ferritin level in the 3rd trimester resulting in failure of ferritin to decrease is correlated with very preterm delivery and markers of maternal infections. Underlying this association are iron deficiency and other indicators of poor maternal nutritional status earlier in pregnancy.

         


    The presence of high concentrations of serum ferritin measured at 28 weeks gestational age raises the possibility that such a determination may allow selection of subset of women at a risk for very low birthweight infants, which might be prevented by a trial of antibiotics. It is an important clue that deserves extensive randomised prospective study.

        

  • A Fetal Systemic Inflammatory Response is followed by the Spontaneous Onset of Preterm Parturition. 

    R Romero, et al (Wayne State Univ, Detroit; Natl Inst. Of Child Health and human Development, Bethesda, Md; Seoul Natl Univ Korea; et al ). 

    Am J Obstet Gynecol 179:186-193, 1998.

        


    The relationship between fetal plasma interleukin (IL-6) concentration and the onset of spontaneous preterm labour in patients with preterm premature rupture of the membranes was assessed.

        


    Results: Fetuses of patients who delivered within 48 hours were significantly more likely than those of patients who delivered in more than 48 hours to have plasma IL-6 concentrations greater than 11 pg/ml (58% vs 8%). The more common infective organism isolated was ureaplasma urealyticum.

         


    Conclusion: Fetal plasma IL-6 level is a significant risk factor for severe neonatal morbidity.

         


    Editorial comments: The incidence of histologic chorioamniotis (44%) is far larger than the incidence of culture-positive amniotic fluid which is about 26% or of clinical chorioamnionitis (9.6%). This probably represents the ability of interleukin 8 (IL-8) present in meconium to evoke an acute inflammatory response in the absence of infection. There is clearly more work to be done before their findings can be employed in clinical management, but the relationships they describe are very important.

        

  • 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.


       

      



 

 

Speciality Spotlight

 

 

Preterm Labour
   

  • TO Scholl (Univ of Medicine and Dentistry of New Jersey, Stratford
    High third trimester ferritin concentration: Associations with very preterm delivery, infection, and maternal nutritional status.) 
    Obstet Gynecol, 92:161-166, 1998.
        
    Very preterm delivery is caused by sub clinical maternal infections. Prospective follow up study included 1162 gravidas with a high serum ferritin levels at week 28.
        
    High serum ferritin level in the 3rd trimester resulting in failure of ferritin to decrease is correlated with very preterm delivery and markers of maternal infections. Underlying this association are iron deficiency and other indicators of poor maternal nutritional status earlier in pregnancy.
         
    The presence of high concentrations of serum ferritin measured at 28 weeks gestational age raises the possibility that such a determination may allow selection of subset of women at a risk for very low birthweight infants, which might be prevented by a trial of antibiotics. It is an important clue that deserves extensive randomised prospective study.
        

  • A Fetal Systemic Inflammatory Response is followed by the Spontaneous Onset of Preterm Parturition. 
    R Romero, et al (Wayne State Univ, Detroit; Natl Inst. Of Child Health and human Development, Bethesda, Md; Seoul Natl Univ Korea; et al ). 
    Am J Obstet Gynecol 179:186-193, 1998.
        
    The relationship between fetal plasma interleukin (IL-6) concentration and the onset of spontaneous preterm labour in patients with preterm premature rupture of the membranes was assessed.
        
    Results: Fetuses of patients who delivered within 48 hours were significantly more likely than those of patients who delivered in more than 48 hours to have plasma IL-6 concentrations greater than 11 pg/ml (58% vs 8%). The more common infective organism isolated was ureaplasma urealyticum.
         
    Conclusion: Fetal plasma IL-6 level is a significant risk factor for severe neonatal morbidity.
         
    Editorial comments: The incidence of histologic chorioamniotis (44%) is far larger than the incidence of culture-positive amniotic fluid which is about 26% or of clinical chorioamnionitis (9.6%). This probably represents the ability of interleukin 8 (IL-8) present in meconium to evoke an acute inflammatory response in the absence of infection. There is clearly more work to be done before their findings can be employed in clinical management, but the relationships they describe are very important.
        

  • 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.

       

      

 

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