Comparison of vaginal breech deliveries with and without magnetic resonance imaging in primigravidas: a retrospective cohort analysis and literature review.

Purpose: Pelvimetry is often recommended in primiparous patients before offering vaginal breech delivery. Later studies show a reduction in perinatal mortality in women undergoing pelvimetry while earlier studies show the opposite. Magnetic resonance imaging (MRI), considered a new technology in 1990, has become the more expensive method for pelvimetry with lower-radiation, believed to prevent unnecessary cesarean sections and "falsely attempted vaginal deliveries".

Methods: This retrospective cohort study (November 2019-February 2024) involved 160 primigravidas with breech presentation. The deliveries were attended by a team of experienced obstetricians (defined as attending at least 20 vaginal breech deliveries per year). Our cohort without MRI was compared with four study cohorts with MRI that were also used in a 2022 systematic review assessing delivery outcomes.

Results: Neonatal outcomes, cesarean section rate and vaginal delivery rate were compared. Umbilical artery pH was significantly lower in two study cohorts (Hoffmann et al. 2016 7.18 vaginal vs. 7.24 caesarean section (p < 0.001), our cohort 7.19 vaginal vs. 7.27 cesarean section (p < 0.001)). The vaginal delivery rate without MRI (our cohort) was 65.6%. In studies with prior MRI as a selection criterion, the rate was between 65.4% and 67.5% (Hoffmann, Van Loon, Klemt). 25.5% of our patients who had to be delivered by cesarean had non-reassuring fetal heart tones in the second stage of labor. Only 4.4% of the patients attempted delivery with epidural anesthesia.

Conclusion: Pelvimetry has not been shown to predict neonatal outcome and there is still no consensus on the interpretation of MRI measurements. Many authors argue, as confirmed by our results, that the outcomes are not dependent on pelvimetry, but on the competence of the obstetric delivering team.