Effect of United States residence on birth outcomes among Mexican immigrants: an exploratory study

Adverse pregnancy outcomes such as low birth weight are increased among US-born mothers of Mexican descent compared with immigrant mothers born in Mexico. It is unknown whether adverse reproductive outcomes change among Mexican immigrants after only 5 years of US residence. The authors conducted a study of 1,114 Mexican immigrant mothers and their infants in two California counties. The relation between US residence status and birth outcomes was examined, controlling for sociodemographic factors and maternal behaviors. Long-term immigrants who have lived in the United States for more than 5 years were more likely to deliver preterm infants (odds ratio (OR) = 1.9, 95% confidence interval (CI) 1.1-3.3) and low birth weight infants (OR = 1.5, 95% CI 0.8-2.7) than newcomers who have lived in the United States for 5 years or less. Long-term immigrants had higher parity, more pregnancy complications, and fewer planned pregnancies, and were more likely to smoke than newcomers. After controlling for confounders, the effect of residence status on preterm delivery was of borderline significance (adjusted OR = 1.8, 95% CI 1.0-3.2). Pregnancy complications was an intervening variable between residence status and preterm delivery. Length of US residence is associated with an increase in low birth weight via a decrease in gestational age rather than intrauterine growth retardation.