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Preterm Birth and Birthweight-for-Gestational Age among Immigrant Women in Denmark 1978–2007: A Nationwide Registry Study


Grete S. Pedersen, Department of Epidemiology, Institute of Public Health, University of Southern Denmark, JB Winsløws Vej 9, 5000 Odense C, Denmark. E-mail:


Background:  We sought to examine whether age at immigration and length of residence were associated with preterm and small-for-gestational age (SGA) delivery among immigrant women in Denmark.

Methods:  We included all live singleton deliveries from Danish-born women (1 626 880) and women from the five largest immigrant groups (68 936) from 1978 to 2007. Data from the Danish Medical Birth Registry were linked to: parental country of origin, length of residence and age at immigration. Linear and logistic regression models were used to estimate absolute and relative differences with Danish-born women as the reference group.

Results:  All immigrant groups had an increased risk of SGA delivery with the highest risk among Lebanese-, Somali- and Pakistani-born women: risk differences (RDs) and 95% confidence intervals [CI] per 1000 deliveries of 50.2 [95% CI 43.7, 56.7], 70.1 [95% CI 62.2, 77.9] and 85.7 [95% CI 78.5, 92.9]. Turkish- and Pakistani-born women had increased RDs of 1.8 [95% CI 0.5, 3.1] and 2.2 [95% CI 0.1, 4.2] for very preterm and RDs of 3.5 [95% CI 0.9, 6.1] and 10.2 [95% CI 5.9, 14.5] for moderate preterm delivery. Lebanese-born women had a decreased risk of very preterm delivery, RD of −1.9 [95% CI −3.5, −0.3] and Somali-born women a lower risk of moderate preterm delivery, RD of −7.8 [−12.0, −3.6]. No differences were seen for the remaining groups. The association with length of residence for most immigrant groups was U-shaped, with highest risks among recent and long-term residents.

Conclusion:  Immigration was more strongly related to SGA than to preterm delivery. Observed differences in birth outcomes varied by age at immigration and length of residency in Denmark.