Maternal pre‐pregnant body mass index, maternal weight change and offspring birthweight

Abstract

To estimate the association between maternal pre-pregnant body mass index (BMI) and maternal weight change during pregnancy and offspring birthweight using the BMI classification developed by World Health Organization (WHO) and adopted by the Institute of Medicine (IOM) in 2009. The Norwegian Mother and Child Cohort Study (MoBa) is a population-based pregnancy cohort study conducted by The Norwegian Institute of Public Health. Women were recruited from all geographic areas of Norway. The study includes 58,383 pregnant women. Women were enrolled in 2000-2007 by a postal invitation offered to women in Norway at 17-18 weeks of gestation. Linear regression analyses are based on exposure data from two questionnaires during pregnancy and on birthweight data. Birthweight. Mean pre-pregnancy BMI was 24kg/m(2) (SD 4.3), mean maternal weight change in the first 30 weeks of gestation was 9.3kg (SD 4.4), mean birthweight was 3675g (SD 487) and mean age 30.3 years. Of the women, 65.2% had a normal pre-pregnancy weight, 2.9% were underweight, 22.3% overweight, and 9.5% obese (Classes 1-3). Linear regression analyses adjusted for potential confounders showed that offspring birthweight increased with increasing maternal pre-pregnant BMI, and with increasing maternal weight gain during pregnancy in all six categories of pre-pregnancy BMI. Women with the highest level of education had the highest offspring birthweight. Offspring birthweight increased with both increasing maternal pre-pregnant BMI and maternal weight gain during pregnancy in all six categories of maternal pre-pregnancy BMI.