Perinatal risk factors are associated with lung function and respiratory symptoms in adult life. Whether the same holds for distinctive asthma features, such as bronchial hyperresponsiveness (BHR) and atopy, has scarcely been studied.

We sought to identify the perinatal risk factors for the development of BHR and atopy.

BHR and atopy were measured after 20 years' follow-up in 597 of 3162 babies born from 1975 through 1978. Factors directly related to delivery of these children were studied in association with the presence of BHR and atopy.

Twenty-five percent had BHR, and 47% had atopy. Delivery duration of longer than 12 hours was associated with the development of atopy (odds ratio [OR], 2.24; 95% CI, 1.30-3.86), and severe respiratory infection in the first year of life was associated with the development of BHR (OR, 2.69; 95% CI, 1.41-5.16). Nonatopic subjects born after induced labor and current smokers were more likely to have BHR (ORs of 2.41 [95% CI, 1.07-5.41] and 2.50 [95% CI, 1.12-5.59], respectively). Prenatal smoke exposure and childhood pet keeping decreased the risk for atopy, especially in BHR-positive subjects (ORs of 0.51 [95% CI, 0.27-0.99] and 0.46 [95% CI, 0.24-0.88], respectively).

It has been shown that events before or during birth still have an effect on respiratory health 20 years later. We put forward that an extreme hormonal status during delivery primes the fetal immune system toward atopy development. Furthermore, a severe respiratory infection in the first year of life appears associated with BHR development, and prenatal smoke exposure might be protective for the development of atopy, yet explanatory mechanisms are lacking thus far.