The weight of inequalities: Duration of residence and offspring's birthweight among migrant mothers in Sweden.

In this study we assessed the effect duration of residence on the association between maternal origin and birthweight in Sweden. Considering sibling information, we also investigated how far the presence or lack of such an effect could be biased by the use of cross-sectional data, since there may be a selection among those mothers who decide to have a child soon after moving to the country (e.g. those with a more stable family situation). Using the Swedish Medical Birth Register for the period 1992-2012, we performed linear and multinomial regressions, multilevel linear regressions, and random effect meta-analysis. Offspring of foreign-born mothers were lighter on average (-120 g [-143,-60]) and had a higher risk of having low birthweight (RRR:1.70 [1.61,1.80]) compared to those with Swedish-born mothers. The variation of birthweight by duration of residence was small (less than 50 g) compared to the gradient found between countries grouped according to the human development index (HDI), where the difference between countries with low and very high HDI was of 105 g. Moreover, no clear pattern toward a convergence with the Swedish population was observed after nine years in the country, which was confirmed when we compared the between- and within-mother analyses by HDI categories. Overall, our results support the thesis that contextual early life conditions have an impact on adult health (reproductive health in this case) with consequences in the next generation that cannot be buffered by the situation experienced in the host country.