The Impact of Change in Pregnancy Body Mass Index on Macrosomia

Objective: To examine the impact of change in body mass index (BMI) during pregnancy on the incidence of macrosomia. Methods: This is a retrospective cohort study using 2007 linked birth certificate and discharge diagnosis data from the state of California. Adjusted odds ratios (aOR) with 95% confidence intervals (CI) were calculated for the outcome of macrosomia, as a function of a categorical change in pregnancy BMI: BMI loss (< -0.5), no change (-0.5 to 0.5), minimal (0.6 to 5), moderate (5.1 to 10), and excessive (> 10). The impact of pregnancy change in BMI was determined for the entire cohort and then stratified by prepregnancy BMI category. Minimal BMI change served as the reference group. Results: The study population consisted of 436,414 women. Overall, women with moderate and excessive BMI changes had aORs of 1.66 and 3.21, respectively, for macrosomia, when compared with women with minimal BMI change. When stratified by prepregnancy BMI, normal (aOR 3.85) and overweight women (aOR 2.96) with antenatal BMI change greater than 10 had the highest odds of macrosomia. Conclusions: Excessive change in pregnancy BMI results in an increased odds of macrosomia. This finding was most pronounced in the normal and overweight women.