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Abstract

Despite global progress in reducing maternal mortality, severe maternal morbidity (SMM; life-threatening complications during pregnancy or the postpartum period) remains a concern, with rates rising in several high-income countries. As population characteristics shift, and major events such as the COVID-19 pandemic reshape healthcare delivery, ongoing surveillance is essential. This thesis examines: 1) SMM case-fatality rates, 2) temporal trends in SMM, 3) trends in hypertensive disorders of pregnancy (HDPs, which may lead to SMM), and 4) risk factors for severe HDPs. In Canada (excluding Quebec) from 2015/16 to 2021/22, the SMM rate was 18.5 per 1,000 deliveries (95% confidence interval [CI] 18.3-18.7), with a case-fatality rate of 2.12 per 1,000 SMM cases (95% CI 1.67-2.65). Cardiac conditions and assisted ventilation had the highest case-fatality rates. SMM rates increased from 17.6 in 2015/16 to 19.6 per 1,000 deliveries in 2021/22, driven by increases in severe hemorrhage, hysterectomy, and acute renal failure, while surgical complications, sepsis, and cerebrovascular accidents declined. After pandemic onset, the overall SMM trend was unchanged; however, sepsis rates declined by 1.9% per month (95% CI: 0.6-3.3) and assisted ventilation rates increased by 2.2% per month (95% CI 0.7–3.7). In British Columbia, gestational hypertension increased from 48.1 to 77.7 per 1,000 pregnancies between 2012/13 and 2023/24, while preeclampsia rose from 17.6 to 41.6 per 1,000 pregnancies. After adjustment for maternal risk factors, increasing trends persisted for chronic hypertension, gestational hypertension, preeclampsia, preeclampsia superimposed on chronic hypertension, and severe preeclampsia/eclampsia (SPE), while HELLP (hemolysis, elevated liver enzymes, low platelets) syndrome declined. Pandemic onset was associated with transient declines in preeclampsia and superimposed preeclampsia. Twin pregnancies carried a 6.6-fold higher risk of severe HDPs (SPE/HELLP) than singleton pregnancies (relative risk 6.61, 95% CI 5.84-7.49). Some risk factors differed by plurality: high body-mass-index (BMI) and in-vitro fertilization (IVF) were associated with elevated risk in singleton pregnancies only, while a history of prior abortions was associated with decreased risk in twin pregnancies only. These studies describe the current landscape of SMM and HDPs in Canada, identify areas for improvement, and provide clinically relevant information to guide risk assessment and prevention.