Maternal predictors of birthweight: The importance of weight gain during pregnancy

To investigate the importance of maternal weight gain during pregnancy as a predictor of birthweight.

Two thousand and forty-six mother-infant pairs were recruited in 1984-1985 from 14 maternity units from the Stockholm Pregnancy and Weight Development Study.

Weight gain during pregnancy (WGP), smoking, pre-pregnancy BMI, gestational diabetes, hypertension, parity, marital status, age, and sex of the child were investigated as predictors of birthweight by multiple regression analysis. WGP was analysed as a continuous and categorical variable, with the latter defined according to the Institute of Medicine (IOM) recommendations as inadequate (n = 501), adequate (n = 860) or excessive (n = 535).

The predictors studied explained 25% of the variance in birthweight. After adjustment for gestational age, WGP (both categorical and continuous) was an important independent predictor of birthweight. Infants of mothers with excessive weight gain had higher birthweight (139 g; 95%CI 83, 196) than infants to mothers with adequate weight gain. In contrast, birthweight was lower for infants of mothers with inadequate weight gain (-148 g; 95%CI -202, -93). Measured as a continuous variable the infants became 26 g heavier for each kilogram the mother gained in weight. In addition, smoking, parity, sex and BMI also showed a positive association to birthweight. Hypertension contributed only marginally and the impact of marital status and maternal age did not reach statistical significance.

As WGP is both an important and modifiable risk factor for abnormal birthweight, and recommendations exist for different BMI groups, it seems natural to put further emphasis on advising pregnant women to stay within the recommended ranges.