Severe maternal morbidity from conception to 6 weeks postpartum in Ontario: a population-based, longitudinal cohort study

Background — Although severe maternal morbidity (SMM), such as severe hemorrhage and sepsis, can occur from conception to 6 weeks postpartum, most surveillance studies in Canada are restricted to intrapartum cases, with rates approximating 17 per 1000 births. We aimed to characterize the frequency of SMM from conception to 6 weeks postpartum and describe its associations with maternal and clinical characteristics.

Methods — We conducted a population-based cohort study of births at 20 or more weeks’ gestation, using administrative data in Ontario (2012 to 2021), and identified SMM using the Canadian Perinatal Surveillance System definition. We assessed the frequency of SMM overall, by period of occurrence (antepartum, intrapartum, and 6 weeks postpartum), and by SMM types. For each period, we described crude associations between characteristics identified a priori and SMM, using logistic regression.

Results — Among 1 095 228 births, the SMM rate was 27.24 per 1000 births; 15.63%, 55.02%, and 29.34% of cases occurred antepartum, intrapartum, and postpartum, respectively. The most common SMM types were severe hemorrhage overall (6.10 per 1000 births), acute abdomen antepartum (1.94), severe hemorrhage intrapartum (5.28), and sepsis postpartum (4.69). Characteristics associated with SMM varied across periods. For example, whereas the frequency of intrapartum and postpartum SMM showed a U-shaped relationship with maternal age, antepartum SMM was associated with ages 15 to 19 years (v. 25 to 34 yr; odds ratio 2.22, 95% confidence interval 1.91 to 2.58) but not 40 to 49 years.

Interpretation — In Ontario, SMM affects nearly 3% of pregnancies between conception and 6 weeks postpartum. Extending the usual observation window showed that approximately 40% of cases of SMM occurred outside the intrapartum period, which would support measures to strengthen recognition of SMM from conception through the postpartum period.