Performance of a Maternal Risk Stratification System for Predicting Low Apgar Scores

Abstract

Objective: Maternal risk stratification systems are increasingly employed in predicting and preventing obstetric complications. These systems focus primarily on maternal morbidity, and few tools exist to stratify neonatal risk. We sought to determine if a maternal risk stratification score was associated with neonatal morbidity. Study Design: Retrospective cohort study of patients with liveborn infants born at ≥24 weeks at four hospitals in one health system between 1/1/2020-12/31/2020. The Expanded Obstetric Comorbidity Score (EOCS) used as the maternal risk score. The primary neonatal outcome was 5-minute Apgar <7. Logistic regression models determined associations between EOCS and neonatal morbidity. Secondary analyses were performed, including stratifying outcomes by gestational age and limiting analysis to “low-risk” term singletons. Model discrimination assessed using the area under the receiver operating characteristic curves (AUC) and calibration via calibration plots. Results: 14,497 maternal-neonatal pairs were included. 236 (1.6%) had 5-minute Apgar <7. EOCS were higher in 5-minute Apgar <7 group (median 41 vs. 11, p<0.001). AUC for EOCS in predicting Apgar <7 was 0.72 (95% CI 0.68, 0.75), demonstrating relatively good discrimination. Calibration plot revealed that those in the highest EOCS decile had higher risk of neonatal morbidity (7.6% vs. 1.7%, p<0.001). When stratified by gestational age, discrimination weakened with advancing gestational age: AUC 0.70 for <28 weeks, 0.63 for 28-31 weeks, 0.64 for 32-36 weeks, and 0.61 for ≥37 weeks. When limited to term low-risk singletons, EOCS had lower discrimination for predicting neonatal morbidity and was not well calibrated. Conclusions: A maternal morbidity risk stratification system does not perform well in most patients giving birth, at low risk for neonatal complications. The findings suggest the association between EOCS and 5-minute Apgar <7 likely reflects a relationship with prematurity. This study cautions against intentional or unintentional extrapolation of maternal morbidity risk for neonatal risk, especially for term deliveries.