To estimate the association between an abnormal pelvic dimension at pelvimetry and the occurrence of severe neonatal morbidity after trial of labor after cesarean (TOLAC).

Retrospective observational cases-controls study conducted at a level 3 maternity units between 2006 and 2016. Included women were patient with trial of labor after one previous cesarean section, alive singleton fetus in cephalic presentation ≥ 37WG. Two groups were compared according to pelvic mesures at pelvimetry: pelvic dimension considered as abnormal, defined by Conjugate Diameter <10.5cm and/or Transverse Diameter <12cm and pelvic dimension considered as normal for other women. The primary outcome was a composite criterion of neonatal morbidity and mortality. A logistic multivariate regression model was use to estimate the association between an abnormal pelvic dimension at pelvimetry and the occurrence of severe neonatal morbidity.

2474 women were included. 863 (34.8 %) have a normal pelvic dimension and 1611 (65.2 %) an abnormal. Characteristics of labor were similar in two groups. Success of TOLAC was 84.7 % in normal pelvic group and 64.6 % in abnormal dimension of pelvic group. Neonatal morbidity was similar between two groups (1.7 % in normal pelvic dimension group versus 2.3 % in abnormal pelvic dimension group, p=0.26; crude OR: 1.39 (0.77–2.49) ; adjusted OR : 0.93 (0.51–1.68)).

There were no association between pelvic dimension at pelvimetry and neonatal morbidity. In case of abnormal pelvic dimension, a combination of more prudence, and stringent user practices, achieve a high rate of vaginal delivery and a neonatal morbidity comparable to the normal pelvic dimension group.