Objective: To assess the incidence and risk factors of asthma and atopic dermatitis by seven years of age after early-term (ET) (37(+0)-38(+6) weeks), full-term (FT) (39(+0)-40(+6) weeks), late-term (LT) (41(+0)-41(+6) weeks), and especially post-term (PT) (42 weeks) birth.

Methods: Altogether, 965203 infants born between 1991 and 2008 in Finland were investigated in ET, FT, LT, and PT groups. Data on asthma medication reimbursement and hospital visits for atopic dermatitis were retrieved from national health databases.ResultsThe frequencies of asthma medication reimbursement in the ET, FT, LT, and PT groups were 4.5%, 3.7%, 3.3%, and 3.2%, respectively. Hospital visits due to atopic dermatitis were most common after PT birth. Compared with FT births, ET births were associated with an increased risk of asthma (adjusted odds ratio (aOR), 95% confidence interval (CI) 1.20, 1.17-1.23), while LT (aOR, 95%CI 0.91, 0.89-0.93) births and PT (aOR, 95%CI 0.87, 0.83-0.92) births decreased this risk. PT birth (aOR, 95%CI 1.06, 1.01-1.10) predicted atopic dermatitis. From a population point of view, the most relevant risk factors for asthma were male sex, ET birth, smoking during pregnancy and birth by elective cesarean section, and for atopic dermatitis male sex, first delivery, birth in a level II hospital and birth by cesarean section.

Conclusions: Early-term birth was a predictor of asthma, and PT birth was associated with atopic dermatitis. Counseling against smoking and following strict indications for planned ET deliveries and cesarean sections may be means to reduce the risk of later asthma.