Differences in birthweight curves between newborns of immigrant mothers vs. infants born in their corresponding native countries: systematic overview.

BACKGROUND: Newborn weight may vary between ethnic groups, but it is not known if birthweight differences exist between term babies born to immigrant mothers compared with those born in their corresponding native countries. METHODS: We completed a systematic review of all birthweight curves published between 1980 and 2012, based on at least 100 singleton deliveries. We compared the 10th, 50th and 90th percentile birthweight values at 40 weeks gestation for male and female infants born in their native country vs. those infants born to mothers who had emigrated from their native country to Ontario, Canada. For the 50th percentile values, we also calculated a standardised pooled weighted difference and 95% confidence interval [CI] for both sexes. We also assessed whether birthweight differed over time, or if the differences varied by the Human Development Index (HDI) value for the native country. RESULTS: A total of 31 studies from 21 different countries met the inclusion criteria, comprising 13 317 578 males and 12 859 119 females born at 40 weeks gestation. There was a small non-significant rise in reported birthweight percentile values between 1983 and 2006. Nearly all infants born to women in their native country had lower birthweights than those born to mothers who had emigrated from the same country to Canada at the 10th, 50th and 90th percentiles. Overall, the 50th percentile weights differed by 115 g [95% CI 74, 156] for males and 122 g [95% CI 95, 150] for females. As HDI or median birthweight increased, birthweight differences were less pronounced, but not significantly so. CONCLUSIONS: Term birthweight percentiles are typically higher among term infants born to mother who immigrate to Canada than those of infants born in their respective native country.