Prepregnancy weight status, prenatal weight gain, and the outcome of term twin gestations.

Relationships among prepregnancy weight status, prenatal weight gain, and the outcome of 922 twin gestations delivered at term were retrospectively investigated with the use of data provided by linked birth-death certificates in Kansas, 1980 to 1986. Infant birth weights were found to increase linearly with prenatal weight gain for women who entered pregnancy underweight and at normal weight, but not for women who were overweight or obese at the start of pregnancy. The rate of twin gestation was twice as high in obese women as that in underweight women. The proportion of infants born with low birth weight declined as prepregnancy weight status increased. The mean prenatal weight gain of underweight women who were delivered of term twin infants with birth weights in the range of lowest perinatal mortality (3001 to 3500 gm) was 44.2 +/- 12.4 pounds. For normal-weight women, the corresponding figure was 40.9 +/- 11.3 pounds. These mean gains were significantly higher than the gains of underweight and normal-weight women who were delivered of smaller infants at term.