Risk of operative delivery for intrapartum fetal compromise in small-for-gestational-age fetuses at term: an internally validated prediction model.

BACKGROUND: Small-for-gestational-age fetuses are at an increased risk of intrapartum fetal compromise requiring operative delivery. Factors associated with the risk of intrapartum fetal compromise are yet to be established, and a comprehensive model accounting for both the antenatal and intrapartum variables is lacking.

OBJECTIVE: We aimed to develop and validate a predictive model for the risk of operative delivery for presumed intrapartum fetal compromise in fetuses suspected to be small for gestational age at term.

STUDY DESIGN: This was a single-center cohort study of small-for-gestational-age fetuses, defined as estimated fetal weight below the 10th centile in singleton pregnancies at term. The variables included known risk factors for operative delivery because of fetal compromise: maternal characteristics, estimated fetal weight, abdominal circumference, Doppler parameters, gestational age at delivery, induction of labor, and intrapartum risk factors (presence of meconium, augmentation of labor using oxytocin, the use of epidural analgesia, intrapartum pyrexia, and hemorrhage). The receiver-operating characteristics curve analysis was used to investigate the predictive accuracy. Internal validation of the models was performed with bootstrapped data sets.

RESULTS: A total of 927 term pregnancies with 18.7% operative deliveries were included. The antenatal model (area under the curve, 0.69; 95% confidence interval, 0.65-0.73) using only the antenatal risk factors included parity, abdominal circumference centile, gestational age at delivery beyond 39 weeks' gestation, and the cerebroplacental ratio multiples of median. The combined model (area under the curve, 0.76; 95% confidence interval, 0.72-0.80), using both the antenatal and intrapartum risk factors, included the gestational age at delivery beyond 39 weeks' gestation (odds ratio, 1.62; 95% confidence interval, 1.14-2.56), the cerebroplacental ratio multiples of median (odds ratio, 0.38; 95% confidence interval, 0.18-0.79), parity (odds ratio 0.35; 95% confidence interval, 0.22-0.54), induction of labor (odds ratio 1.63; 95% confidence interval, 1.11-2.40), augmentation using oxytocin (odds ratio, 1.84; 95% confidence interval, 1.23-2.73) and the use of epidural analgesia (odds ratio, 2.80; 95% confidence interval, 1.94-4.04). The results indicate that the model has good discrimination and, according to the Hosmer-Lemeshow test, has good fit (P = .591).

CONCLUSION: The prediction model demonstrates 6 important risk factors that are associated with the risk of operative delivery for fetal compromise in small-for-gestational-age fetuses at term. The model shows good discrimination and fit and has the potential to be used for clinical decision making and to counsel women about their individual intrapartum risk.