External validation of the Maternal Severity Index for predicting maternal death following potentially life-threatening complications during pregnancy and childbirth: a single-centre, prospective observational study

OBJECTIVES: To perform an external validation to assess the usefulness of the Maternal Severity Index (MSI) in predicting maternal death among women with potentially life-threatening complications during pregnancy or childbirth. DESIGN: Prospective observational study. SETTING: A tertiary referral centre in southeastern India. PARTICIPANTS: 1833 women with potentially life-threatening complications identified using the WHO criteria. PREDICTOR ASSESSED: MSI calculated based on the severity markers of the WHO criteria for maternal near-miss. PRIMARY OUTCOME: Maternal death. STATISTICAL ANALYSIS: Receiver operating characteristics (ROC) curve analysis was performed to assess discriminative performance, and agreement between expected and observed deaths was plotted to determine calibration. RESULTS: The incidence of severe maternal outcomes was 10 per 1000 live births. There were 57 (151 per 100 000 live births) maternal deaths during the study period. Maternal Severity Score was significantly higher among those who died (2.8±1.3 vs 2.0±1.2, p<0.001). The mean MSI value was 1.03% (95% CI 0.7% to 1.2%). ROC curve analysis showed good discrimination (AUC(Area Under the Curve): 0.962, 95% CI 0.952 to 0.970); however, overfitting was seen with higher probabilities. The standardised mortality ratio (SMR) was 0.02 (95% CI 0.01 to 0.02), indicating good quality of care. CONCLUSIONS: The MSI has good discriminative performance in distinguishing who succumbs to life-threatening complications, but needs recalibration to avoid overfitting. SMR of less than 0.5 indicates fewer than expected deaths, suggesting good quality of care in reducing maternal mortality in the study population.