The effect of pregnancy on the body mass index 9 months postpartum in 49 women.

The effect of pregnancy on the body mass index (weight/height2) was studied. The change in the body mass index from pregestation through 9 months postpartum of 49 pregnant women was compared with the change in the body mass index during the same period of follow-up in 400 non-pregnant women. All women participated in a follow-up study in which body weight was measured every 6 months. In addition the body weight of the pregnant women was measured at 6 and 12 months postpartum. Nine months postpartum the total group of pregnant women had gained as much body mass as was to be expected from ageing. The same was true for the subgroup of women who did not breast-feed their child or who breast-fed for a period shorter than 2 months. Unexpectedly, women who breast-fed their child for more than 2 months gained +0.6 kg/m2 (90 per cent CI: +0.1, +1.0) more body mass than the non-pregnant women. Compared to the latter group, women who used bromocriptine to stop lactation lost body mass (-0.5 kg/m2, 90 per cent CI: -1.1, +0.0). These observations suggest that, postpartum, the total group of pregnant women has not gained more body mass than expected from ageing. 'Maternal obesity' may be associated with breast-feeding for long periods.