Optimal gestational weight gain ranges for the avoidance of adverse birth weight outcomes: a novel approach.

BACKGROUND: Gestational weight gain (GWG) has been shown to be directly associated with birth weight.
OBJECTIVE: We aimed to define ranges for optimal GWG with respect to the risk of either small- or large-for-gestational-age offspring by using a new statistical approach.
DESIGN: For the purpose of an observational study, data on n = 177,079 mature singleton deliveries in Bavaria between 2004 and 2006 were extracted from a standard data set that is regularly collected for national benchmarking of obstetric units in terms of clinical performance. Joint predicted risks of either small- or large-for-gestational-age births in relation to GWG (continuous measurement) were estimated by logistic regression models with adjustment for potential confounders.
RESULTS: The estimated optimal GWG ranges as defined by a joint predicted risk of <or=20% were substantially wider than those recommended by the Institute of Medicine for underweight (8-25 compared with 12.5-18.0 kg) and normal-weight (2-18 compared with 11.5-16.0 kg) women. Overweight and obese women's optimal GWG ranged from -7 to 12 and -15 to 2 kg, respectively (Institute of Medicine recommendations: 7.0-11.5 and 5.0-9.0 kg, respectively). We observed considerable effect modifications by parity and smoking in pregnancy. In normal-weight primiparae, for example, the optimal GWG range was 10-26 kg for nonsmokers compared with 23-27 kg for smokers.
CONCLUSIONS: Considerably wider optimal GWG ranges than recommended by the Institute of Medicine might be tolerated with respect to avoidance of adverse birth weight outcome. Stratification by maternal body mass index category alone might not be sufficient.