Low birth weight infants and parental nativity in Singapore: epidemiological paradox in Asia - a nationally representative population-based cohort study.

Background: Despite Singapore's top-ranked healthcare system, the country's low birth weight (LBW) rates exceed the Organisation for Economic Co-operation and Development average. Singapore also has one of the highest proportions of female marriage migrants in Asia, many of whom originate from lower-income neighbouring countries. These marriage migrants often face socioeconomic disadvantages and social integration challenges, and their children tend to exhibit more behavioural problems and lower achievement scores at a young age, raising concerns about potential higher LBW risk in this population. Given the increasing global migration population, this study examines whether foreign-born mothers have higher LBW prevalences than native-born mothers, assesses whether their presence contributes to Singapore's high LBW rates, and explores the contributing factors underlying any observed differences. Methods: Using data from the Singapore Longitudinal Early Development Study, a nationally representative sample of 5005 children born between 2011 and 2019, four family types were identified based on parental nativity: native families; cross-national families with a foreign-born mother; cross-national families with a foreign-born father; and families with both foreign-born parents. Logistic regression was used to measure group differences in LBW prevalence. Fairlie decomposition was applied to quantify the contributions of observed covariates to these differences. Results: Cross-national families with a foreign-born mother had a lower LBW prevalence (OR 0.56, 95% CI 0.37 to 0.86) than native families, even after adjusting for risk factors. Fairlie decomposition showed that 75% of the immigrant health advantage in LBW was explained by observed covariates, driven primarily by mismatches in the quality of healthcare systems between the countries of origin and Singapore, followed by group differences in biological and socioeconomic factors. Conclusions: The findings reveal an epidemiological paradox in Singapore, echoing immigrant health advantages observed in other developed countries: socioeconomically disadvantaged foreign-born mothers had lower LBW rates than native-born mothers. However, this advantage is not uniform and varies by family type and migration background, highlighting the importance of considering immigrant-family heterogeneity in perinatal health research.