• Naila Ramji, Daniel J Corsi, Monica Gad, Sheryll Dimanlig-Cruz, Qun Miao, Yanfang Guo, Natalie Rybak, Ruth Rennicks White, Shi Wu Wen, Mark C Walker, and Laura M Gaudet.
• Department of Obstetrics & Gynecology (Ramji), Dalhousie University, Fredericton, NB; Department of Bioethics (Ramji), Dalhousie University, Halifax, NS; Better Outcomes Registry and Network Ontario (Corsi, Dimanlig-Cruz, Miao, Walker), Children's Hospital of Eastern Ontario (CHEO); CHEO Research Institute (Corsi, Miao), Ottawa, Ont.; Nicotine Dependence Service (Gad), Centre of Addiction and Mental Health, Toronto, Ont.; Clinical Epidemiology Program (Dimanlig-Cruz, Guo, Rybak, Rennicks White, Wen, Walker), Ottawa Hospital Research Institute; School of Epidemiology and Public Health (Guo, Wen), University of Ottawa; Department of Obstetrics, Gynecology & Newborn Care (Rybak, Rennicks White), The Ottawa Hospital, Ottawa, Ont.; Department of Obstetrics and Gynecology (Gaudet), Queen's University; Department of Obstetrics and Gynecology, Kingston Health Sciences Centre (Gaudet), Kingston, Ont. naila.ramji@post.harvard.edu nl182868@dal.ca.
• CMAJ. 2024 Mar 3; 196 (8): E250E259E250-E259.

BackgroundMaternal obesity is associated with stillbirth, but uncertainty persists around the effects of higher obesity classes. We sought to compare the risk of stillbirth associated with maternal obesity alone versus maternal obesity and additional or undiagnosed factors contributing to high-risk pregnancy.MethodsWe conducted a retrospective cohort study using the Better Outcomes Registry and Network (BORN) for singleton hospital births in Ontario between 2012 and 2018. We used multivariable Cox proportional hazard regression and logistic regression to evaluate the relationship between prepregnancy maternal body mass index (BMI) class and stillbirth (reference was normal BMI). We treated maternal characteristics and obstetrical complications as independent covariates. We performed mediator analyses to measure the direct and indirect effects of BMI on stillbirth through major common-pathway complications. We used fully adjusted and partially adjusted models, representing the impact of maternal obesity alone and maternal obesity with other risk factors on stillbirth, respectively.ResultsWe analyzed data on 681 178 births between 2012 and 2018, of which 1956 were stillbirths. Class I obesity was associated with an increased incidence of stillbirth (adjusted hazard ratio [HR] 1.55, 95% confidence interval [CI] 1.35-1.78). This association was stronger for class III obesity (adjusted HR 1.80, 95% CI 1.44-2.24), and strongest for class II obesity (adjusted HR 2.17, 95% CI 1.83-2.57). Plotting point estimates for odds ratios, stratified by gestational age, showed a marked increase in the relative odds for stillbirth beyond 37 weeks' gestation for those with obesity with and without other risk factors, compared with those with normal BMI. The impact of potential mediators was minimal.InterpretationMaternal obesity alone and obesity with other risk factors are associated with an increased risk of stillbirth. This risk increases with gestational age, especially at term.© 2024 CMA Impact Inc. or its licensors.

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