Pregnancy outcome according to pre-pregnancy body mass index and gestational weight gain

To assess birth weight in relation to gestational weight gain (GWG) among women who were and were not obese before pregnancy.

For a retrospective cohort study, data were obtained for women with a pre-pregnancy body mass index (BMI, calculated as weight in kilograms divided by the square of height in meters) of at least 30 who had a singleton delivery at a center in Denmark in 2010-2011. Data were also obtained for 455 non-obese women (BMI 20.0-24.9). GWG was expressed in absolute terms and relative to published recommendations (11-16kg in non-obese women; 5-9kg in obese women).

A total of 231 obese women were included in analyses. In non-obese and obese women, fetal weight was highest when GWG was above the recommended amount. Among women who had a GWG in line with the recommendations, mean birth weight was higher among those with a pre-pregnancy BMI of 35.0-39.9 (3758±410g) or at least 40 (3671±374g) than among non-obese women (3394±453g; P=0.0058).

Birth weight is related to both maternal BMI and GWG. In obese women, adherence to GWG recommendations does not seem to prevent increased birth weights.