637 Gestational age specific risks for obese women with and without other risk factors

Abstract

Obesity is one of the most preventable pre-pregnancy risk factors for adverse perinatal events. Despite this, there are few body-mass-index (BMI) specific prognostic models for timing of delivery associated with the lowest number of adverse perinatal events. Our aim was to build a model to estimate gestational age-specific rates of adverse perinatal outcomes in obese women with and without additional risk factors. This was a retrospective cohort study of all singleton births at ≥34 weeks’ gestation in British Columbia, Canada, 2008-2017. Data were obtained from the British Columbia Perinatal Database Registry. A multivariable Cox proportional hazards model including demographic and obstetric risk factors was used to estimate gestational age specific risk of composite perinatal mortality and severe morbidity for women at various weight classes. Interactions between obesity and other important risk factors were assessed on both the additive and multiplicate scales. Among all women (n=283,697), 13.1% were obese (pre-pregnancy BMI ≥30m/kg2), and 60.1% had normal BMI (18.5-24.9 m/kg2). As a fraction of ongoing pregnancies, adverse outcomes increased with increasing gestational age at delivery in women of all weights. There was a dose-response relationship with increasing BMI with those morbidly obese (BMI ≥ 40m/kg2) at the highest risk. Other key risk factors included nulliparity, chronic hypertension and diabetes mellitus. Obese women with any of these additional risk factors exhibited far worse outcomes than those without with increasing disparities at later delivery. There was additive interaction between nulliparity, chronic hypertension and diabetes mellitus and obesity, but no multiplicate interactions. Obese women are at increased risk of worse perinatal outcomes at all gestational ages. These risks are compounded by other known risk factors of adverse perinatal outcomes, especially closer to term.