Maternal Birthplace is Associated with Low Birth Weight Within Racial/Ethnic Groups.

Introduction While disparities in low birth weight (LBW) incidence by racial/ethnic group are well known, differences in LBW incidence by maternal birthplace within racial/ethnic groups, and particularly, differences after adjustment for pregnancy complications, are less clear. Methods We conducted a population-based study of LBW using 113,760 singleton, live birth records from King County, Washington (2008-2012), a region in the Pacific Northwest with a large immigrant population. Study participants were Asian, non-Hispanic black, Hispanic, Native Hawaiian/Other Pacific Islander (NHOPI), and non-Hispanic white women. Using multivariable logistic regression models, we calculated odds ratios (ORs) and 95% confidence intervals (CIs) to estimate relative risk of LBW (<2500 g) related to maternal race/ethnicity and birthplace (defined by the Millennium Development Goals Regional Groupings). Results Compared with non-Hispanic white women, non-Hispanic black, Asian Indian, Filipino, Japanese, and Vietnamese women had 1.57-2.23-fold higher, statistically significant, risk of having a LBW infant, and NHOPI and Mexican women had 1.30-1.33-fold, statistically significant, higher risk. LBW risk was lower for Asian women from Eastern Asia (OR 0.68, 95% CI 0.55-0.85), non-Hispanic black women from Sub-Saharan Africa (OR 0.58, 95% CI 0.47-0.73), and non-Hispanic white women from other developed countries (OR 0.83, 95% CI 0.69-1.00), as compared with their US-born racial/ethnic counterparts. Results were, in general, similar after adjustment for pregnancy complications. Conclusions Compared with most other racial/ethnic groups, non-Hispanic whites had lower risk of LBW. Foreign-born women had lower risk of LBW compared with their US-born counterparts in the majority of racial/ethnic groups. Pregnancy complications had minimal effect on the associations.