Cerebroplacental ratio thresholds measured within 2 weeks before birth and risk of Cesarean section for intrapartum fetal compromise and adverse neonatal outcome.

OBJECTIVES: Prediction of intrapartum fetal compromise in uncomplicated, term pregnancies is a global obstetric challenge. Currently, no widely accepted screening test for this condition exists, although the cerebroplacental ratio (CPR) shows promise. We aimed to evaluate prospectively the screening performance of the CPR 10th centile threshold for prediction of Cesarean section for intrapartum fetal compromise (IFC) and composite adverse neonatal outcome (ANO) after 36 weeks' gestation in low-risk women, and to compare this with CPR ≤ 1 and < 5th centile thresholds described previously in the literature.

METHODS: This was a blinded, prospective, observational, cohort study of 483 women with uncomplicated singleton pregnancy who underwent fortnightly CPR measurements from 36 weeks to delivery, and their intrapartum and neonatal outcomes were recorded. The CPR 10th centile threshold screening performance was calculated for emergency Cesarean section for IFC and composite ANO (defined as acidosis at birth, 5-min Apgar score < 7 and/or admission to the neonatal intensive care unit). Comparison of screening performance of CPR ≤ 1 and < 5th and < 10th centile thresholds was also undertaken for these specified outcomes.

RESULTS: In total, 437 women were included in the analysis, of whom 4.1% had an emergency Cesarean section for IFC and 17.8% had a composite ANO. Sensitivity and specificity for CPR < 10th centile were, respectively, 55.6% and 87.9% for prediction of Cesarean section for IFC, and 28.2% and 88.0% for composite ANO. Compared with CPR ≤ 1 and < 5th centile, CPR < 10th centile yielded the best overall test performance for detection of Cesarean section for IFC and composite ANO, although its predictive value was only fair for Cesarean section for IFC (area under the receiver-operating characteristics curve (AUC) = 0.72) and poor for composite ANO (AUC = 0.58).

CONCLUSION: The CPR 10th centile threshold may be useful as a component of a risk assessment tool for Cesarean section for IFC in low-risk pregnancies at term. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.