Nathalie Auger, MD, MSc, FRCPC Unité Études et analyses de l'état de santé de la population, Institut national de santé publique du Québec
Zhong-Cheng Luo, MD, PhD, Department of Obstetrics and Gynaecology, Sainte-Justine Hospital, Université de Montréal
Robert W Platt, PhD, Department of Epidemiology and Biostatistics, McGill University
Mark Daniel, PhD, Département de médecine sociale et préventive, Université de Montréal
The epidemiologic paradox has been used to refer to unexpectedly good birth outcomes among low socio-economic groups of foreign-born populations. The healthy migrant effect is described as positive birth outcomes among foreign-born populations. The relation between the epidemiologic paradox and the healthy migrant effect has not been studied. We evaluated the epidemiologic paradox and healthy migrant effect for newborns on the Island of Montreal.
We analyzed 98,330 live births to mothers in Montreal, Canada from 1997 to 2001. Mothers were categorized as foreign-born versus Canadian-born. Three outcomes were evaluated: small for gestational age (SGA) birth; low birth weight (LBW); and preterm birth (PTB). Multi-level logistic regression was used to examine the interaction between maternal education and foreign-born status, adjusting for covariates.
Tests for effect modification show that foreign-born status and socio-economic status interact to influence birth outcomes. Not having a high school diploma was associated with LBW in Canadian [OR = 3.20 (95%CI: 2.61-3.91)] but not foreign-born [OR = 1.14 (95%CI: 0.99-2.10)] mothers, indicating the presence of an epidemiologic paradox. Similarly, not having a high school diploma was more strongly associated with SGA birth in Canadian [OR = 2.03 (95%CI: 1.84-2.22)] than in foreign-born [OR = 1.26 (95%CI: 1.07-1.49)] mothers. With respect to the healthy immigrant effect foreign-born status was associated with SGA birth [OR = 1.37 (95%CI: 1.28-1.47)], LBW [OR = 1.51 (95%CI: 1.27-1.79)], and PTB [OR = 1.12 (95%CI: 1.03-1.22)] in university educated mothers only.
In Montreal, the association between educational attainment and newborn health differs in foreign-born compared to native-born mothers. Likewise, the association between maternal foreign-born status and newborn health varies depending on educational attainment. These differences have implications for policies governing maternal-infant health programs. Public health interventions targeting foreign-born mothers should align with the socio-economic conditions of mothers.