Should delivery timing for repeat cesarean be reconsidered based on dating criteria?

We sought to examine if the method of pregnancy dating at five increasing term gestational ages is associated with increasing neonatal morbidity.

A cohort of women who underwent elective repeat cesarean delivery at ≥37 weeks' gestation were identified from the NICHD MFMU Network registry. We excluded women who were in labor, those carrying a fetus with a congenital anomaly, those with a non-reassuring fetal heart tracing, and those with preeclampsia, preexisting chronic hypertension or diabetes. Composite neonatal morbidity was defined for our study as any of the following: NICU admission, hypotonia, meconium aspiration, seizures, need for ventilator support, NEC, RDS, TTN, hypoglycemia, or neonatal death. We compared composite neonatal morbidity rates among infants born at five different gestational age cutoffs according to their method of pregnancy dating.

At 39 and 40 weeks' gestation, the lowest rate of neonatal complications was seen in pregnancies dated by first trimester ultrasound (5.8% and 5.5%, respectively), while those with the highest neonatal morbidity rates were seen when dated by a second or third trimester ultrasound (8.1% and 6.0%, respectively); p < .001. Additionally within each pregnancy dating category, the neonatal morbidity rates declined from 37 to 40 weeks' gestation and then significantly increased at 41 + 0 weeks' gestation.

Even with suboptimal dating methods, amongst women undergoing elective repeat cesarean delivery, neonatal morbidity was lowest when delivery occurred between 40 and 40 + 6 weeks gestation.