Background: To estimate the risk of hyperemesis gravidarum (HG) among first generation immigrants to Norway by length of residence.
Design: A cross-sectional study.
Methods: The sample consisted of first generation immigrants with a prevalence of HG exceeding ethnic Norwegians by 50%, registered in the Medical Birth Registry of Norway (MBRN). The women were born in Turkey, Middle East, North Africa, Other Africa, Iran, Pakistan, India and Sri Lanka and Central and South America, the total sample size is 50,904. MBRN data on HG, age, parity, plurality and sex of the baby were linked to information on country of birth, maternal education and duration of stay obtained from Statistics Norway. Independent associations were studied for each immigrant group and adjusted for potential confounders. To account for dependencies in the sample, a generalized estimating equations (GEE) approach was used.
Results: For women from Central and South America, adjusted analysis showed a decrease in the risk of HG by longer residency (P for trend = 0.026). A similar but not significant trend was observed for women born in the Middle East (P for trend = 0.097). Women born in Turkey who had been living in Norway for 6-8 years had a higher risk of HG than newcomers, though no trend was observed (P for trend = 0.127). Women born in Iran and North Africa who lived longer in Norway tended to have a higher risk of developing HG than newcomers (P for trend = 0.083 and 0.118, respectively)
Conclusion: Associations between HG and duration of residence in Norway did not show a universal pattern across immigrant groups. Women born in Central and South America had a lower risk of HG with increasing length of residence. Some evidence to the contrary was found for women born in Iran, North Africa and Turkey.