Determinants of birthweight inequalities: Population-based study

Background The aim of this paper is to study the whole spectrum of birthweight in a population-based birth cohort in order to document the role played by social factors, which complement physiological and behavioural factors, in the development of birthweight inequalities at the population level. Methods The analyses were performed with data from the 'Quebec Longitudinal Study of Child Development 1998-2002 (QLSCD)'. The study follows a representative sample (n = 2103) of the children born in 1998 in the Canadian province of Quebec. Results Multivariate analyses adjusted for gestational age and mother's age indicate that mean birthweight was higher for boys than girls; improved with birth rank, mother's body mass index (BMI), and family socioeconomic status; and was lower for children of smoking mothers. Compared with children born to non-smoking mothers of higher socioeconomic status, the odds of having a low birthweight were between 6 and 12 times higher for children born to smoking mothers of lower or middle socioeconomic status. When maternal smoking status and mother's BMI are combined, socioeconomic status could still be seen to have a positive effect on mean birthweight except for overweight or obese smoking mothers, among whom the relationship between socioeconomic status and mean birthweight was reversed. In families of lower socioeconomic status, maternal smoking was the most important factor in birthweight inequalities, and in families of higher socioeconomic status, mother's BMI was the most important factor in birthweight inequalities. Conclusion This research is not only important for children in developed nations, but also for those in developing countries, where high birthweight and obesity are becoming more prevalent.