Pregnancy-Associated Maternal Mortality Within One Year After Childbirth: Population-Based Cohort Study

Objective: The objective of this study is to assess associations between pregnancy complications and pregnancy-associated maternal mortality (PAM) within 1 year after childbirth. Design: Population-based cohort study. Setting: Norway, 1967-2020. Population: 1 237 254 mothers with one or more singleton pregnancies registered in the Medical Birth Registry, 1967-2019 and followed in the Cause of Death Registry to 2020. Methods: Logistic regression was used to calculate odds ratios (ORs) with 95% confidence intervals (CIs), adjusted for maternal education, age, year of first childbirth and chronic medical conditions. Main Outcome Measures: PAM by lifetime history of pregnancy complications: placental abruption, preeclampsia, preterm birth, perinatal death, small for gestational age (< 2.5 percentile), gestational diabetes and gestational hypertension. Results: Crude OR for PAM was 4.24 (95% CI 3.53-5.10), if complications occurred in the last pregnancy, whereas 2.52 (2.08-3.06) if complications occurred in the first pregnancy, compared to mothers without complications in any pregnancy. Adjusted ORs for PAM when complications occurred in the last pregnancy were, for placental abruption 3.75 (1.20-11.72), preeclampsia: 4.42 (3.17-6.15), preterm birth: 4.32 (3.25-5.75), perinatal death: 24.18 (16.66-35.08), small for gestational age: 2.90 (1.85-4.54), gestational diabetes: 1.43 (0.63-3.25) and pregnancy hypertension: 2.05 (1.12-3.74) compared to mothers without complications. The OR for PAM increased slightly by increasing the number of complicated pregnancies but the trend was stronger for increasing number of complications in the last pregnancy (e.g., during 1999-2019: one complication; 4.14 [2.79-6.13], two complications; 11.50 [6.81-19.43]). Conclusion: Complications in the last pregnancy were more strongly associated with PAM than those in the first pregnancy.