Value of routine ultrasound examination at 35–37 weeks' gestation in diagnosis of non‐cephalic presentation

Background: Undiagnosed non-cephalic presentation in labor carries increased risks for both the mother and baby. Routine pregnancy care based on maternal abdominal palpation fails to detect the majority of non-cephalic presentations.

Objective: To report the incidence of non-cephalic presentation at a routine scan at 35+0 - 36+6 weeks’ gestation and subsequent management of such pregnancies.

Methods: This was a retrospective analysis of prospectively collected data in 45,847 singleton pregnancies that had undergone routine ultrasound examination at 35+0 - 36+6 weeks’ gestation. Patients with breech or transverse / oblique presentation were divided into two groups, first those that would have elective cesarean section for fetal or maternal indications other than the abnormal presentation, and second, those that would potentially require ECV. The latter group was reassessed in 1-2 weeks and if there was persistence of the abnormal presentation the parents were offered the options of ECV versus elective cesarean section at 38-40 weeks’ gestation. Multivariable logistic regression analysis was carried out to determine which of the factors from maternal and pregnancy characteristics provided a significant contribution in the prediction of first, non-cephalic presentation at the 35+0 - 36+6 weeks scan, second, successful ECV from non-cephalic to cephalic presentation, and third, spontaneous rotation from non-cephalic to cephalic presentation.

Results: First, at 35+0 - 36+6 weeks the fetal presentation was cephalic in 43,416 (94.7%) pregnancies, breech in 1,987 (4.3%) and transverse or oblique in 444 (1.0%). Second, multivariable analysis demonstrated that the chance of non-cephalic presentation increased with increasing maternal age and weight, decreasing height, earlier gestational age at scan, and it was higher in the presence of placenta previa, oligohydramnios and polyhydramnios, in nulliparous than parous women and lower in women of South Asian and mixed racial origin than in White women. Third, 22% of cases of non-cephalic presentation were not eligible for ECV because of planned cesarean section for indications other than the malpresentation. Fourth, of those eligible for ECV only 48.5% (646/1,332) accepted the procedure and this was successful in 39.0% (252/646) of cases. Fifth, the chance of successful ECV increased with increasing maternal age and was lower in nulliparous than parous women. Sixth, in 33.9% (738/2,179) of pregnancies with non-cephalic presentation where successful ECV was not carried out there was a subsequent spontaneous rotation to cephalic presentation. Seventh, the chance of spontaneous rotation from non-cephalic to cephalic presentation increased with increasing interval between the scan and delivery and decreased with increasing birth weight, it was higher in women of Black than White racial origin, if the presentation was transverse or oblique than breech and if there was polyhydramnios and lower in nulliparous than parous women and in the presence of placenta previa. Eighth, in 109 (0.3%) of cephalic presentations there was subsequent rotation to non-cephalic presentation and in 41% of these the diagnosis was made during labor. Ninth, in the total of 2,431 cases of non-cephalic presentation at the time of the scan the presentation at birth was cephalic in 985 (40.5%); in 738 (74.9%) this was due to spontaneous rotation and in 247 (25.1%) due to successful ECV. Tenth, prediction of non-cephalic presentation at the 35+0 - 36+6 weeks scan and successful ECV from maternal and pregnancy factors was poor, but prediction of spontaneous rotation from non-cephalic to cephalic presentation was moderately good and this could be incorporated in the counselling of women prior to undertaking ECV.

Conclusions: The problem of unexpected non-cephalic presentation in labor can to a great extent be overcome by a routine ultrasound examination at 35+0 - 36+6 weeks’ gestation. The incidence of non-cephalic presentation at the 35+0 - 36+6 weeks scan was about 5%, but, in about 40% of these cases the presentation at birth was cephalic, mainly due to subsequent spontaneous rotation and to a lesser extent as a consequence of successful ECV.

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