Prediction of obstetric outcome in vaginal breech birth using ultrasound pelvimetry in nulliparous women—A feasibility study

Abstract Introduction Magnetic resonance (MR) pelvimetry is widely used in planning vaginal breech birth and may support women's informed decision‐making regarding their preferred mode of birth. This feasibility study aimed to assess whether transperineal ultrasound (TPU) could measure the maternal pelvis as accurately as MR pelvimetry and thus predict the outcome of vaginal breech birth. Material and Methods In this prospective cohort study, nulliparous women with a singleton fetus in breech presentation received TPU for the measurement of the anteroposterior mid‐pelvic diameter (AMD). These measurements were compared with those in MR pelvimetry to assess agreement and reliability. In women choosing to attempt vaginal breech birth, we additionally examined the association between the AMD (adjusted for possible confounders) and intrapartum cesarean section. The predictive performance of the AMD and traditional pelvic diameters (i.e., obstetric conjugate, interspinous, and intertuberous distance) was compared by means of the area under the receiver operating characteristic curve (AUC). Results Overall, 67 nulliparous women with breech presentation received both TPU and MR pelvimetry, of which 47 chose a vaginal breech birth (30 successful vaginal births and 17 intrapartum cesarean sections). The repeatability coefficients and intraclass correlation coefficient for the AMD were 0.38 cm and 0.97 (95% CI 0.96–0.98), respectively. Bland–Altman analysis between the AMD measured in TPU and MR pelvimetry yielded a mean difference of −0.0052 cm (95% CI −0.066 to 0.056 cm) with upper and lower limits of agreement of 0.48 cm (95% CI 0.38–0.59 cm) and −0.49 cm (95% CI −0.6 cm to −0.39 cm), respectively. In the subgroup of women who attempted vaginal breech birth, AMD was significantly associated with intrapartum cesarean section (adjusted odds ratio 0.25; 95% CI 0.06–0.81; AUC 0.77), while the obstetric conjugate, interspinous, and intertuberous distances were not. Conclusions TPU can accurately and reliably measure the AMD, a novel pelvic diameter in breech presentation. Importantly, a smaller AMD was associated with an increased risk of intrapartum cesarean section if vaginal breech birth was attempted. Consequently, TPU could represent an alternative to MR pelvimetry and support women in deciding their preferred mode of birth in breech presentation.