Impact of Pre-Pregnancy Body Mass Index and Gestational Weight Gain on Preterm Birth [6A]

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This study was undertaken to evaluate the differential impact of pre-pregnancy body mass index (PPBMI) and gestational weight gain (GWG) on preterm birth (PTB).


Vital statistics (birth) data collected by the National Center for Health Statistics (NCHS) was utilized. Using the 2015 data for singleton gestations, GWG was calculated and PPBMI was categorized as per WHO guidelines. Each PPBMI category was further stratified based on the adequacy of GWG - into inadequate, adequate and excess GWG subgroups using the 2009 IOM guidelines. Multivariate logistic regression analyses were used to predict the risk for preterm birth (<37 weeks) in each PPBMI and GWG group while adjusting for age, race, education, marital status, insurance and smoking status.


The rate of preterm birth was noted to be 7.65% (276,820/3,619,295 deliveries). In comparison to women with adequate GWG, those with inadequate GWG [OR = 1.637 (95% CI 1.621 – 1.653)] had an overall increased risk for PTB across all PPBMI categories. Specifically, inadequate GWG was noted to increase the risk for PTB in normal weight [OR = 1.976 (95% CI 1.948 – 2.004)], underweight [OR = 2.384 (95% CI 2.286 – 2.486)], overweight [OR = 1.435 (95% CI 1.404 – 1.468)] and obese women [OR = 1.161 (95% CI 1.138 – 1.185)] as compared to women in the matched PPBMI categories with adequate GWG in the adjusted regression analyses.


In this cohort, weight gain outside of the IOM recommendations was noted to significantly impact the risk for PTB across all PPBMI categories.

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