Aug. 4, 2010 -- Women who put on too many pounds during pregnancy are at risk of having a baby with a high birth weight, which may increase the child’s risk for long-term obesity, researchers report.
High birth weight is associated with a higher body mass index (BMI) -- a measurement of height and weight -- later in life. However, researchers were not clear whether weight gain during pregnancy contributed to a child’s risk of obesity independently of genetics. Earlier research suggests maternal weight is more strongly associated with a child’s BMI than paternal weight, indicating that pregnancy, not only genetics, may play a key role in a child’s weight.
Researchers at Children’s Hospital in Boston and Columbia University in New York looked at multiple single pregnancies in the same mother to assess the effects of maternal weight gain and to exclude the effects of weight gain from genetic components.
The authors found a consistent connection between weight gain during pregnancy and bigger babies. Among their findings reported in the Aug. 5 issue of The Lancet:
For every kilogram (kg) a mother gained (1 kg = 2.2 lbs), the baby’s birth weight increased by 7.35 grams (0.25 oz).
Compared with infants born to women who gained between 8 kg and 10 kg (17.5 and 22 lbs), infants born to mothers who gained more than 24 kg (52.5 lbs) during pregnancy were about 150 g (5.3 oz) heavier at birth.
Mothers who gained more than 24 kg during pregnancy were more than twice as likely to deliver a baby weighing 4,000 grams (8 lbs 13 oz) or more, compared with women who gained only 8 kg to 10 kg.
The findings are based on state birth registry data from Michigan and New Jersey. Researchers analyzed information on 513,501 women and their 1,164,750 children born between January 1989 and December 2003. Pregnancies shorter than 37 weeks or more than 41 weeks, women who had diabetes, infants born weighing less than 500 grams or more than 7,000 grams, and anyone missing data for pregnancy weight gain were excluded from the study. The study was supported by the National Institutes of Health.