A new study which appears in the September 30 issue of The Lancet finds that a woman who gains even a small amount of weight between pregnancies significantly increases her risk of a poor pregnancy outcome.
Reseachers used the records of more than 150,000 Swedish women who had first and second consecutive births from 1992 through 2001. They calculated body mass index, or B.M.I., at the beginning of the first pregnancy and again at the start of the second.
Compared with women who gained less than one unit of B.M.I. between pregnancies, those who gained three or more were twice as likely to have gestational diabetes, 76 percent more likely to have gestational hypertension, 30 percent more likely to have a Caesarean delivery and 63 percent more likely to have a stillbirth. The more weight they gained the more likely they were to have an adverse outcome.
The authors acknowledged that since the time between births varied from 1 to 10 years, some of the weight gain could be due to temporary postpartum weight retention and that there could be unmeasured factors that might have affected both weight gain and pregnancy outcome.
“The strongest evidence of causality would come from a randomized clinical trial, but that’s obviously not possible here,” said Eduardo Villamor, the lead author of the study and an assistant professor at the Harvard School of Public Health. “One alternative is to look at changes in exposure over time and to find out if they are associated with changes in risk, and that’s what we did. For now, we believe that the results allow us to conclude that weight gain in women of normal B.M.I. between pregnancies is not advisable.