Comparison of indicators for severe maternal morbidity among South Korean women who delivered from 2003 to 2018: a population-based cohort study

Abstract Background: Previous studies of the relationship between severe maternal morbidity (SMM) and risk factors used only a single indicator for SMM and did not compare the various SMM indicators and the incidence differences with each. This study aimed to identify risk factors for SMM by reviewing four international SMM indicators and ascertaining the differences in SMM incidence in South Korea with each indicator.Methods: This study used the National Health Insurance delivery cohort in South Korea from 2003 to 2018. SMM was estimated using four indicators: the United States Centers for Disease Control and Prevention (US-CDC) SMM algorithm, the American College of Obstetricians and Gynecologists (ACOG) gold standard guidelines, Zwart et al.’s indicators for the Netherlands, and the European Network on Severe Acute Maternal Morbidity (EURONET-SAMM) index. Generalized estimating equations models were used to identify the relationships between SMM indicators and risk factors.Results: The SMM incidence rates in 6,421,091 deliveries, were 2.36%, 3.12%, 0.31%, and 1.36% using the US-CDC, ACOG, Zwart et al.’s, and EURONET SAMM indicators, respectively. In sub indicators, hemorrhage-related codes constituted the highest proportion of all SMM indicators. Advanced maternal age was related to high risk in all four SMM indicators (US-CDC: 40-44 years, RR 1.67, 95% CI 1.63-1.71; ACOG’s guidelines: 40-44 years, RR 1.52, 95% CI 1.49-1.56; Zwart’s indicators: RR 2.72, 95% CI 2.55-2.90; EURONET-SAMM: RR 2.04, 95% CI 1.97-2.11) compared to those aged 25-29 years. In residential area, women who lived in rural area had approximately 1.2- to 1.5-fold higher risk of SMM compared to those who lived in Seoul. Additionally, inadequate prenatal care was associated with a 1.1- to 1.4-fold higher risk of SMM compared to adequate prenatal care. Conclusions: SMM was associated with maternal age, socioeconomic status, and adverse obstetric factors using various international SMM indicators. Further studies are needed to further determine risk and preventable factors for SMM and to identify more specific causes associated with the frequent sub-indicators of SMM.