Prepregnancy weight, inappropriate gestational weight gain, and smoking: Relationships to birth weight.

This study was designed to test predictors of infant birth weight based on categories of prepregnancy body mass index (BMI), gestational weight gain, and smoking. Data were collected retrospectively from records of 233 mother-infant pairs enrolled in the Siouxland Women, Infants, and Children (WIC) Program in Sioux City, Iowa. Prepregnancy BMI and gestational weight gain were coded according to Institute of Medicine guidelines. Smoking behavior was coded based on reported smoking during the last 3 months of pregnancy. Multiple regression analysis was used to test predictors of infant birth weight. Forty-two percent of women gained more weight than recommended, and 16% gained less than recommended. Based on prepregnancy BMI, women were classified as underweight (12%), overweight (16%), or obese (31%). Twenty-four percent of mothers reported smoking late in gestation. Higher birth weight was predicted by prepregnancy obesity (+144 g). Lower infant birth weight was predicted by lower (-162 g) and higher (-153 g) than recommended weight gain, and by lower (-299 g) and higher (-168 g) levels of smoking. Depression of birth weight among women who gained excess weight may relate to inadequate early weight gain or pregnancy complications. More research is needed regarding physiological consequences of these maternal factors and their associated demographic risk factors.