Effects of pre-pregnancy physical activity and maternal BMI on gestational weight gain and birth weight

Background. Western women frequently exhibit excessive gestational weight gain (GWG). The effects of maternal physical activity level (PAL) and body mass index (BMI) on the timing of GWG are insufficiently known. Purpose. To assess the impact of pre-pregnancy PAL and BMI on GWG during the second and third trimester and on birth weight. Methods. Body weight was measured in 223 healthy Swedish women in gestational weeks 12, 25 and 33, and GWG during the second (weeks 12-25) and third trimesters (weeks 25-33) was determined (kg/week). PAL was assessed using a questionnaire. Birth weights were obtained from birth records. The results were evaluated by the fitting of linear statistical models. Results. Some 50 and 80% of the women exhibited excessive GWG during the second and third trimesters, respectively. Women with a high pre-pregnancy PAL gained 0.10 kg/week (p=0.04) less weight during the third trimester than women with a medium PAL. A 5 kg/m2 higher BMI was associated with a 0.06 kg/week lower GWG in the second trimester (p=0.005), but with a 0.05 higher GWG in the third trimester (p=0.03). Maternal BMI (p=0.014) and total GWG (p=0.05) correlated with birth weight. Conclusions. High BMI and low pre-pregnancy PAL were associated with excessive GWG. BMI and GWG, but not pre-pregnancy PAL, were linked to birth weight. However, together with smoking, parity, education and age, pre-pregnancy PAL and BMI explained only 4% of the variation in GWG. Thus, identification of other factors that could explain excessive GWG is an important area of future research.