A population-level analysis of birth weight indices in Peel Region, Ontario: the impact of ethnic diversity.

OBJECTIVES The purpose of this paper is to examine whether the elevated rate of low birth weight (LBW) in the Region of Peel, Ontario can be attributed to the high proportion of immigrants in the population. In addition, we examined how the infant birth weight distribution in Peel differs by maternal region of birth. METHODS Provincial live birth registration data were used to compare rates of LBW, preterm birth and small-for-gestational-age (SGA) births in Peel and Ontario for the years 2002 through 2006 by maternal region of birth. Birth weight for gestational age curves were developed for singletons and were specific for infant sex and maternal region of birth using the lambda-mu-sigma (LMS) method. Quantile regression was used to examine whether the median birth weight at term (37 to 42 weeks) differed by maternal region of birth. RESULTS The rate of LBW was higher in Peel than in Ontario (6.8% and 6.0%, respectively). This is the result of a higher SGA rate and not due to differences in rates of preterm birth. Infants of immigrant mothers had significantly lower median birth weights at all gestations, showing that the birth weight distribution among infants of immigrant mothers is shifted towards lower birth weights. CONCLUSION At the population level, the shifted birth weight distribution among singleton infants of immigrant mothers has significant impact on the LBW rate observed in Peel.