Asymmetric pelvis and term breech presentation: is planned vaginal delivery still a safe option?

Purpose: To evaluate the obstetrical prognosis of term breech delivery in case of asymmetric pelvis.

Methods: An observational, comparative, retrospective, bi-centric study of 559 patients who had a computer tomography pelvimetry prior to delivery of a term breech presentation was conducted between August 2013 and August 2019. Patients with an attempted vaginal delivery were divided into two groups: a group of asymmetric pelvis (AP) when the difference between the lengths of both oblique diameters was ≥ 1 cm and a group of symmetric pelvis (SP) when the two oblique diameters differed by < 1 cm. The primary outcome was the rate of vaginal delivery. Secondary outcomes were a composite variable of neonatal and maternal morbidity and mortality.

Results: Of the 370 patients who attempted a vaginal breech delivery, 8% (n = 29) had an AP and 92% (n = 341) had a SP. In the AP group, the vaginal delivery rate was higher (93% versus 78%, p = 0.05). There was no statistically significant difference in neonatal (3% versus 1% in the AP and SP groups, respectively, p = 0.4) and maternal (17% versus 23% in the AP and SP groups, respectively, p = 0.5) morbidity and mortality.

Conclusion: When a pelvimetry is performed before an attempt of vaginal breech delivery, a difference of less than two centimetres between both oblique diameters does not seem to reduce the rate of vaginal birth and is not an indication for an elective caesarean section.