The differential effect of foreign-born status on preterm birth: a Taiwan population-based birth registry study.

Whether foreign-born status confers a protective effect on preterm birth in Taiwan was investigated using singleton live birth data from the 2004 Taiwan Birth Registry (n = 211,946). Newborns of foreign-born mothers (FBMs) comprised 13.7% of the population. The preterm birth rate of newborns of FBMs (5.9%) was significantly lower than that of newborns of Taiwan-born mothers (TBMs) (8.0%) (P < 0.0001). After having adjusted for predisposing maternal factors or adverse pregnancy conditions, newborns of FBMs still had a lower risk in preterm birth than that of TBMs, with an odds ratio of 0.74 and 95% confidence interval between 0.71 and 0.79. Selection was hypothesised to explain the low preterm birth rate in FBMs.