Pre-pregnancy weight, pregnancy weight gain associated with offspring birth weight

Koepp UM. Acta Obstet Gynecol Scand. 2011;doi:10.1111/j.1600-0412.2011.01321.x.

Maternal weight pre-pregnancy and maternal weight gain during pregnancy were associated with offspring birth weight, according to researchers in Norway.

The researchers used data from the Norwegian Mother and Child Cohort Study (MoBa), a population-based pregnancy cohort study by the Norwegian Institute of Public Health, which included women from all geographic areas of Norway.

The study included 58,383 pregnant women who enrolled from 2000 to 2007 by a postal invitation that was offered to women in Norway at 17 to 18 weeks’ gestation. The study involved two questionnaires, one offered at 17 to 18 weeks’ gestation and one at gestational week 30. The researchers used information from the Medical Birth Registry of Norway for the study to identify birth weights.

The women were categorized by BMI pre-pregnancy. There were six groups: underweight, normal weight, overweight, obese class I, obese class II and obese class III. Maternal weight change was calculated from the maternal self-reported weight at gestational age 30 weeks and pre-pregnancy weight.

The mean pre-pregnancy BMI was 24, and the mean maternal weight change in the first 30 weeks of gestation was 9.3 kg. The mean birth weight was 3,675 g. Pre-pregnancy weight was normal in 65.2% of the mothers, 2.9% were underweight, 22.3% were overweight and 9.5% were obese.

Offspring birth weight increased with increasing pre-pregnancy maternal BMI and increasing weight change during pregnancy. For every increase of 1 kg in pre-pregnancy BMI, there was an increase in birth weight of 25.9 g (95% CI, 25.0-26.9). For every 1 kg of maternal weight gain during pregnancy, birth weight increased by 22.4 g (95% CI, 21.5-23.3). These increases were seen across all six categories of pre-pregnancy BMI.

“The implication of this study is that pre-pregnant BMI alone is an important predictor of birth weight,” the researchers wrote. “Furthermore, weight gain during pregnancy has an effect on offspring birth weight independent of pre-pregnancy BMI. An obvious goal should be to encourage overweight and obese women to attain healthy weight before conception and keep a moderate weight gain during pregnancy.”

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