Sonographic fetal head circumference is associated with trial of labor after cesarean section success

The purpose is to study the association of the fetal sonographic head circumference (SHC) with trial of labor after cesarean (TOLAC) success rate, among women with no prior vaginal deliveries.

A retrospective case-control study including all women with no prior vaginal delivery undergoing TOLAC during 3/2011-6/2020 with a sonographic estimated fetal weight within one week from delivery. TOLAC success and failure groups were compared.

Of 1232 included women, 948 (76.9%) delivered vaginally. The mean fetal SHC was smaller in the TOLAC success group (330 ± 10 vs. 333 ± 11 mm, p < 0.001). In a multivariate regression analysis, predelivery BMI, hypertensive disorders, gestational age at prior CD, SHC and epidural analgesia administration were independently associated with TOLAC success. A ROC analysis of the multivariable model composed of the factors found independently associated with TOLAC success, excluding SHC, yielded an area under curve of 0.659 (95% CI 0.622-0.697) compared with 0.668 (95% CI 0.630-0.705) with SHC included.

Smaller SHC is independently associated with TOLAC success among women that did not deliver vaginally before, and has additive clinical value for the prediction of TOLAC success when combined with non-sonographic factors.