• Sarka Lisonkova, Giulia M Muraca, Jayson Potts, Jessica Liauw, Wee-Shian Chan, Amanda Skoll, and Kenneth I Lim.
• Department of Obstetrics and Gynaecology, University of British Columbia and the Children's and Women's Hospital and Health Centre of British Columbia, Vancouver, Canada.
• JAMA. 2017 Nov 14; 318 (18): 177717861777-1786.

ImportanceAlthough high body mass index (BMI) is associated with adverse birth outcomes, the association with severe maternal morbidity is unclear.ObjectiveTo examine the association between prepregnancy BMI and severe maternal morbidity.Design, Setting, And ParticipantsRetrospective population-based cohort study including all singleton hospital births in Washington State, 2004-2013. Demographic data and morbidity diagnoses were obtained from linked birth certificates and hospitalization files.ExposuresPrepregnancy BMI (weight in kilograms divided by height in meters squared) categories included underweight (<18.5), normal BMI (18.5-24.9), overweight (25.0-29.9), obesity class 1 (30.0-34.9), obesity class 2 (35.0-39.9), and obesity class 3 (≥40).Main Outcomes And MeasuresComposite severe maternal morbidity or mortality included life-threatening conditions and conditions leading to serious sequelae (eg, amniotic fluid embolism, hysterectomy), complications requiring intensive care unit admission, and maternal death. Logistic regression was used to obtain adjusted odds ratios (ORs) and adjusted rate differences with 95% confidence intervals, adjusted for confounders (eg, maternal age and parity).ResultsOverall, 743 630 women were included in the study (mean age, 28.1 [SD, 6.0] years; 41.4% nulliparous). Prepregnancy BMI was distributed as follows: underweight, 3.2%; normal weight, 47.5%; overweight, 25.8%; obesity class 1, 13.1%; obesity class 2, 6.2%; and obesity class 3, 4.2%. Rates of severe maternal morbidity or mortality were 171.5, 143.2, 160.4, 167.9, 178.3 and 202.9 per 10 000 women, respectively. Adjusted ORs were 1.2 (95% CI, 1.0-1.3) for underweight women; 1.1 (95% CI, 1.1-1.2) for overweight women; 1.1 (95% CI, 1.1-1.2) for women with class 1 obesity; 1.2 (95% CI, 1.1-1.3) for women with class 2 obesity; and 1.4 (95% CI, 1.3-1.5) for women with class 3 obesity compared with women with normal BMI. Absolute risk increases (adjusted rate differences per 10 000 women, compared with women with normal BMI) were 28.8 (95% CI, 12.2-47.2) for underweight women, 17.6 (95% CI, 10.5-25.1) for overweight women, 24.9 (95% CI, 15.7-34.6) for women with class 1 obesity, 35.8 (95% CI, 23.1-49.5) for women with class 2 obesity, and 61.1 (95% CI, 44.8-78.9) for women with class 3 obesity.Conclusions And RelevanceAmong pregnant women in Washington State, low and high prepregnancy BMI, compared with normal BMI, were associated with a statistically significant but small absolute increase in severe maternal morbidity or mortality.

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