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Abstract

Despite advances in obstetric practice and medical intervention, progress in reducing severe maternal morbidity (SMM) and maternal mortality has been limited in recent decades, partly because of an increase in high-risk pregnancies. This dissertation focuses on four areas contributing or related to this challenge, i) SMM among pregnancies of Assisted Reproductive Technology (ART); ii) SMM among pregnant women with a Solid Organ Transplant (SOT); iii) maternal mortality among women with chronic disease; and iv) issues related to cause-of-maternal death assignment. Among women undergoing ART in Canada (excluding Quebec) in 2009-2018, the composite SMM rate was 34.7 versus 11.5 per 1000 deliveries among women not using ART (rate ratio 3.01, 95% confidence interval [CI] 2.89-3.14). Adjustment for maternal characteristics attenuated this association slightly (adjusted rate ratio 2.34; 95% CI 2.24-2.45). The composite SMM rate among women with SOT in Canada (excluding Quebec), 2003-2018, was 134.5 versus 9.97 per 1,000 deliveries in the non-SOT group (rate ratio 13.5, 95% CI 10.1-18.0). Adjusting for maternal characteristics did not alter this risk (adjusted odds ratio 10.8; 95% CI 7.60-15.3). Assessment of the contribution of chronic diseases to maternal deaths in the United States showed that chronic disease-associated deaths contributed substantially to maternal mortality: they increased by 28% (95% CI 17-40) from 5.41 in 1999-2002 to 6.92 per 100,000 live births in 2018-2022. Cause-of-maternal death assignments have been traditionally based on the underlying cause, whereas modern models of causation favour assignment based on multiple causes. In 2018-2022, pre-eclampsia and hemorrhage were the most common causes of maternal death under the underlying- and rankings under the two approaches, respectively, and cause of death rankings under the two approaches were not correlated (0.62, P value 0.19). Clinical and public health programs to reduce maternal mortality may be more effective if cause-of-death rankings were determined based on multiple causes of death. The first three of the studies in this thesis highlight key aspects of the clinical and population health landscape influencing SMM and maternal mortality in Canada and the United States, and the last study highlights an approach that could improve program effectiveness aimed at preventing maternal mortality.