Preterm birth and birthweight-for-gestational age among immigrant women in Denmark 1978-2007: a nationwide registry study.
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 (1626880) and women from the five largest immigrant groups (68936) 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.


CONCLUSIONS
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.
Department of Epidemiology Department of Biostatistics, Institute of Public Health, University of Southern Denmark. gspedersen@health.sdu.dk
Grete S
GS
Pedersen
Laust H
LH
Mortensen
Mette
M
Gerster
Janet
J
Rich-Edwards
Anne-Marie N
AM
Andersen
D000367:Age Factors; D001724:Birth Weight / Q000502:physiology*; D003718:Denmark; D054242:Emigrants and Immigrants / Q000706:statistics & numerical data*; D005260:Female; D005865:Gestational Age; D006801:Humans; D007230:Infant, Low Birth Weight / Q000502:physiology; D007231:Infant, Newborn; D007236:Infant, Small for Gestational Age / Q000502:physiology; D011247:Pregnancy; D047928:Premature Birth; D012042:Registries; D012044:Regression Analysis; D012111:Residence Characteristics / Q000706:statistics & numerical data; D012306:Risk; D013997:Time Factors