BACKGROUND: Limited information is available about the burden of severe maternal morbidity (SMM) among low-risk pregnancies, which has prevention implications. We assessed proportion of SMM by comorbidity status among Massachusetts delivery hospitalizations to describe how distribution of risk changed over time.
METHODS: The Massachusetts Pregnancy to Early Life Longitudinal (PELL) data system links infant birth certificates and fetal death records to the corresponding maternal and infant hospital discharge records for Massachusetts resident mothers during 1998–2013. SMM was identified from PELL delivery-related hospital discharge records by using CDC’s SMM algorithm; blood transfusion was excluded because of concerns about specificity. PELL deliveries were assigned a comorbidity score (range: 0–45) on the basis of maternal age and International Classification of Disease, Ninth Edition clinical modification codes by using a validated index that predicts maternal morbidity. Mean yearly comorbidity score and overall proportions of SMM by comorbidity score were calculated.
RESULTS: A total of 1,185,182 delivery hospitalizations and 5,325 SMM occurred in Massachusetts during 1998–2013. A total of 687,406 (58%) delivery hospitalizations and 1,358 (26%) SMM had a comorbidity score of zero. Rate of SMM/10,000 delivery hospitalizations increased from 50 in 2008 to 65 in 2013; the mean yearly comorbidity score increased from 0.58 (σ = 0.95) in 1998 to 0.78 (σ = 1.14) in 2013. Rate of SMM/10,000 delivery hospitalizations by comorbidity score ranged from 20 (score = 0) to 1,942 (score ≥10).
CONCLUSIONS: Approximately one quarter of SMM occur among deliveries without comorbidities in Massachusetts, indicating that all levels of birth facility need to anticipate SMM occurrences. The increasing mean delivery comorbidity score during 1998–2013 is consistent with the increasing statewide SMM rate.