Obesity and weight change related to parity and breast-feeding among parous women in Brazil.

OBJECTIVE Studies on the independent role of parity in long-term body weight change in economically developing countries are scarce and inconclusive, and only a few studies have taken into account patterns of breast-feeding. This association was examined in a national cross-sectional survey representative of Brazilian parous women. DESIGN AND SETTING The survey conducted in 1996 measured women's height and weight in the household and data on weight prior to the first pregnancy, parity and breast-feeding were recalled. SUBJECTS A sample of 2338 parous women, 15 to 49 years of age, 29 months after last delivery on average, had current body mass index (BMI, in kg m(-2)) modelled through hierarchical multiple linear regression analysis. Explanatory variables included parity, days of predominant breast-feeding, BMI pre-pregnancy, socio-economic, geographic, demographic and other reproductive variables. RESULTS Prevalences of overweight (BMI = 25.0-29.9 kg m(-2)) and obesity (BMI > or = 30.0 kg m(-2)) were 25.2% and 9.3%. The overall mean weight gain per year after the first pregnancy was 0.90 kg for an average time since first pregnancy of eight years. BMI pre-pregnancy modified the association between current BMI and parity. Therefore, weight change attributed to parity calculated for a woman of average height (1.56 m) was 0.60 kg greater for primiparous women with a BMI pre-pregnancy of 30 kg m(-2), compared with women with BMI pre-pregnancy of 25 kg m(-2). This greater weight retention among obese women was 1.21 kg for women with two children and 1.82 kg for women with three or more children. Parity reduced the effect of weight loss associated with lactation (1.75 kg for six months of lactation among primiparous women and 0.87 kg among women with three or more children). For the sub-sample of 793 primiparous women, a weight decrease of 300 g was associated with each month of predominant breast-feeding for all prior BMI levels. CONCLUSIONS In this study, weight change associated to reproduction was highly dependent on BMI previous to pregnancy and the effects of parity and lactation were small.