Intergenerational transmission of the healthy immigrant effect (HIE) through birth weight: A systematic review and meta-analysis.

This review examines intergenerational differences in birth weight among children born to first-generation and second-generation immigrant mothers and the extent to which they vary by country of origin and receiving country. We searched MEDLINE, EMBASE, Web of Science, PubMed, and ProQuest from inception to October 2014 for articles that recorded the mean birth weight (in grams) or odds of low birth weight (LBW) of children born to immigrant mothers and one subsequent generation. Studies were analyzed descriptively and meta-analyzed using Review Manager 5.3 software. We identified 10 studies (8 retrospective cohort and 2 cross-sectional studies) including 158,843 first and second-generation immigrant women. The United States and the United Kingdom represented the receiving countries with the majority of immigrants originating from Mexico and South Asia. Six studies were meta-analyzed for mean birth weight and seven for low birth weight. Across all studies, there was found to be no statistically significant difference in mean birth weight between first and second-generation children. However, the odds of being LBW were 1.21 [95% CI, 1.15, 1.27] times greater among second-generation children. Second-generation children of Mexican descent in particular were at increased odds of LBW (OR = 1.47 [95% CI, 1.28, 1.69]). In the United States, second-generation children were at 34% higher odds of being LBW (OR = 1.34 [95% CI, 1.13, 1.58]) when compared to their first-generation counterparts. This effect was slightly smaller in the United Kingdom (OR = 1.18 [95% CI, 1.13, 1.23]). In conclusion, immigration to a new country may differentially influence low birth weight over generations, depending on the mother's nativity and the country she immigrates to.