Pregnancy complications and the risk of asthma among Norwegians born between 1967 and 1993.

Background: Fetal life events may affect the development of the immune and/or respiratory system and increase the risk of asthma and allergic diseases. The objective of this study was to test the hypothesis that pregnancy complications are associated with the risk of developing asthma in the off-spring.
Methods: The study population comprised Norwegian live births 1967-1993 (n = 1,548,429) linking the Medical Birth Registry of Norway (MBRN) (exposure variables) and the National Insurance Administration Register (NIAR) (outcome variables), which covers all Norwegians. The MBRN variables included pregnancy complications, pregnancy outcomes and diseases of the mother. The NIAR provided data on all Norwegians who had received cash benefit for treatment of asthma from 1967 to 1996 (n = 5938, 3.9/1000 persons).
Results: In multiple logistic regression analysis, pregnancy complications (International Classification of Diseases (ICD)-8-codes: 630-634) were associated with the risk of asthma (odds ratio 1.82, 95% confidence interval: 1.67-1.98). This was also the case if analyses were performed in different strata according to year of birth, plurality, maternal atopy, geographical district of birth, and maternal education.
Conclusions: Pregnancy complications may represent risk factors for the development of asthma in the offspring or express early signs of increased risk for developing the disease.