Advanced maternal age and severe maternal morbidity in South Korea: a population-based cohort study

To investigate the association between maternal age and severe maternal morbidity (SMM) in a Korean population. Data for cases of delivery between 2003 and 2019 were extracted from the Korean National Health Insurance Service-National Delivery Cohort. The main outcome was SMM, which was determined using the Center for Disease Control and Prevention's algorithm. A generalized estimating equation model with a log link was performed for the relationship between SMM and maternal age adjusted for covariates. SMM occurred in 40,959/2,113,615 (1.9%) of delivery cases. Teenagers and women 35 years and older had an increased risk of SMM in both nulliparous and multiparous cases (ages 15-19: risk ratio (RR) 1.32, 95% confidence interval (CI) 1.15-1.46; ages 35-39: RR 1.24, 95% CI 1.21-1.28; ages 40-44: RR 1.57, 95% CI 1.50-1.64; and ages 45 or older: RR 2.07, 95% CI 1.75-2.44). Women aged 40 years and older had the highest rates of SMM. In singleton births as well as in nulliparous and multiparous cases, teenagers and women aged 35 years and older had a particularly high risk of SMM. Identifying and managing risk factors for SMM in these vulnerable age groups may improve maternal health outcomes.