ATLANTA – A risk score derived from five maternal and fetal parameters can help determine the overall risk of cesarean delivery in nulliparous women at term, according to findings from the prospective multicenter Genesis Study.
The score can be used to better inform patients of their individualized cesarean delivery risk in early pregnancy and late pregnancy, facilitating patient decision making about place and mode of delivery, Dr. Naomi Burke of the Royal College of Surgeons in Dublin, Ireland, reported at the annual Pregnancy Meeting sponsored by the Society for Maternal-Fetal Medicine.
Dr. Naomi Burke
Of 2,336 nulliparous women with a vertex presentation after 39 weeks’ gestation who were recruited for the Genesis Study, 491 had an unplanned C-section. On multivariate analysis, several factors were found to be associated with risk for cesarean delivery, and the combination of maternal age, maternal height, body mass index, fetal abdominal circumference, and fetal head circumference were found to be the best combined predictors of cesarean delivery, Dr. Burke said.
At the initial visit, the odds ratios for the maternal parameters were 1.22 for maternal age, -1.59 for maternal height, and 1.32 for body mass index. After 39 weeks’ gestation the odds ratios were 1.21, -1.72, and 1.29 for those parameters, respectively. The odds ratios were 1.23 for fetal abdominal circumference and 1.27 for fetal head circumference.
Individual z scores were calculated for demographic and biometric data to determine the odds ratios and a risk score for cesarean delivery. The individual scores were added to give a total risk score, which was then converted into a probability of cesarean delivery, Dr. Burke explained. The prediction model performed well in a bootstrapped cross-validation study, she said.
Actual outcomes “were almost exactly as predicted” in different risk categories. “For example, in a cohort of 614 women who had a 30%-40% risk of cesarean delivery, the actual cesarean delivery rate was 26%,” she said.
Further, of 52 women with a risk score over 50% for cesarean delivery, the actual rate was 56%. Among 23 women who had a vaginal delivery, 15 required an operative vaginal delivery, 5 had an obstetric anal sphincter injury, and 1 had shoulder dystocia with a fractured clavicle.
“So you can see that although these women avoided intrapartum cesarean, there was still significant maternal and neonatal morbidity associated,” she said.
The findings are important because cesarean delivery rates continue to generate concern and prior efforts to predict risk for unplanned cesarean delivery have failed. Despite extensive research and costly interventions, it has been unclear which women would suffer the greatest difficulty in childbirth, she said.
The current findings could change that.
“We can now tell, using our prediction model, which women are at high risk of unplanned cesarean delivery,” she said, noting that a randomized, controlled trial is already underway to assess how the implementation of this model can be used to assess maternal and neonatal morbidity.
The Genesis study is sponsored by Perinatal Ireland. Dr. Burke reported having no disclosures.