604: Fetal biometry to predict labor dystocia indicated term primary cesarean delivery: NICHD fetal growth studies

Abstract

Labor dystocia is the commonest indication of primary cesarean delivery (PCD). Our objective was to determine whether fetal biometry obtained close to delivery was associated with or predicted term labor dystocia-indicated PCD in a low risk population. Analysis of a prospective multicenter NIH-sponsored study. Women with a non-anomalous and uncomplicated singleton gestation delivering at ≥37 0/7 weeks were included. Serial sonographic exams with the final exam at 37.5 +/- 1.9 weeks were performed. Estimated fetal weight (EFW), individual biometric parameters, derived fetal asymmetry measurements (i.e. biparietal diameter (BPD) - abdominal diameter (AD) difference), and amniotic fluid deepest vertical pocket measured at this last scan and categorized as < 10th, 10th- 90th(reference), >90th percentiles were compared between women who had labor dystocia-indicated PCD versus spontaneous vaginal delivery. Multivariable logistic regression analysis was conducted to assess the association of fetal biometry with labor dystocia-indicated PCD. A model providing optimal predictive ability measured by area under the curve (AUC) was determined. Of 1,472 pregnancies analyzed, 126 (8.5%) had labor dystocia-indicated PCD. Compared to the reference group, EFW and head circumference (HC) >90th, and BPD-AD difference < 10th percentile doubled the odds of labor dystocia-indicated PCD (Table). A model that included fetal HC >90th percentile (OR [95% CI]: 3.00 [1.34, 6.71]), maternal age (1.08 [1.03,1.13]), gestational weight gain (1.06 [1.02,1.10]), gestational age at delivery (1.26 [0.97, 1.64]), induction of labor (1.76 [1.03, 3.01]), and nulliparity (21.95 [8.59, 56.11]) predicted labor dystocia-indicated PCD with an AUC of 0.84. Sensitivity, specificity, positive and negative predictive values of this model were 76%, 76%, 23%, and 97%, respectively. Several fetal biometric parameters were associated with labor dystocia-indicated PCD. Large fetal HC (>90th percentile) at term along with multiple maternal factors constituted the best predictive model of labor dystocia-indicated PCD.