Maternal body mass index change as a new optimal gestational weight gain predictor in overweight women.

Aim: To investigate the relationship between maternal pre-pregnancy body-mass index (BMI) and neonatal birth weight.

Methods: The observational study included 2906 mothers and their neonates born from 2005 to 2011 at the Department of Gynecology and Obstetrics, Split University Hospital Center. Mothers with singleton term pregnancies who were overweight before pregnancy (BMI 25-29.9 kg/m2) were compared with those with normal pre-pregnancy weight (BMI 18.5-24.9 kg/m2). BMI change was assessed as a predictor of birth weight, categorized as small (SGA), appropriate (AGA), or large for gestational age (LGA).

Results: The rate of SGA infants was significantly lower (n=199; 6.8% vs n=1548; 9.2%) and the rate of LGA infants significantly greater among pre-pregnancy overweight mothers compared with normal-weight mothers (n=371; 12.8% vs n=1302; 7.8%; P<0.001 both). Overweight mothers had a significant probability of delivering an SGA neonate when they gained less than 6 kg, as compared with 8 kg among normal-weight mothers. They had a significant probability of delivering an LGA neonate when they gained more than 14 kg, compared with more than 20 kg among normal-weight mothers. BMI change was a more consistent indicator, suggesting that the ranges of 3.0-7.9 kg/m2 in overweight and 2-5.9 kg/m2 in normal-weight women were not associated with a significant increase in the rate of SGA or LGA.

Conclusion: Maternal height seems to be an important factor in optimal weight gain definition, suggesting that BMI change should be a preferred measure of pregnancy-related weight.