Background: Perinatal conditions may be associated with future allergic disease; however, data are conflicting and incomplete for childhood allergic rhinitis (AR). The aim of this study was to examine pregnancy outcome (cesarean delivery, preterm birth, low birthweight) and offspring AR as defined by national registers.

Methods: Nationwide longitudinal cohort study using prospectively recorded register data from 1 059 600 singleton livebirths born in Sweden in 2001-2012. Cox regression adjusted for infant sex and maternal factors (age at delivery, country of birth, parity, smoking, body mass index, and asthma/pulmonary disease) estimated hazard ratios (HRs) for AR during childhood.

Results: During the study period 2001-2013, 22 386 (2.11%) children were diagnosed with AR. AR was more common in infants born through cesarean delivery (2.34%) than in those born vaginally (2.10%) (HR = 1.12; 95% confidence interval [95% CI] = 1.08-1.16). This was equivalent to one extra case of AR in 383 children followed up in our study. AR was also associated with moderately preterm birth (>= 32-36 weeks of gestation: HR = 1.12, 95% CI = 1.04-1.20), large for gestational age (HR = 1.05, 95% CI = 1.01-1.10), and low (<7) 5-minute Apgar score (HR = 1.15, 95% CI = 1.02-1.30). Similar risk estimates were obtained when we restricted the outcome to >= 2 hospital-based records of AR. No association was observed between very preterm birth, post-term birth, low birthweight, or small for gestational age and AR. Conclusion Our study indicates an association between pregnancy outcomes and childhood AR, although observed effect sizes were generally modest.

Background: Immunoglobulin E (IgE) sensitization is associated with asthma and allergic diseases. Gestational age influences early immune system development, thereby potentially affecting the process of tolerance induction to allergens.

Objective: To study IgE sensitization to common allergens by gestational age from childhood up to early adulthood.

Methods: Population-based birth cohort, data from the Swedish BAMSE study were used. Allergen-specific IgE antibodies to a mix of common food (fx5) and inhalant (Phadiatop) allergens were analysed at 4, 8, 16 and 24 years. Sensitization was defined as allergen-specific IgE >= 0.35 kU(A)/L to fx5 and/or Phadiatop at each time point. Using logistic regression and generalized estimated equations, adjusted odds ratios (aORs) for sensitization in relation to gestational age were calculated. Replication was sought within the Swedish twin study STOPPA.

Results: In BAMSE, 3522 participants were screened for IgE antibodies during follow-up; of these, 197 (5.6%) were born preterm (<37 gestational weeks) and 330 (9.4%) post-term (>= 42 weeks). Preterm birth reduced the risk of sensitization to common food and/or inhalant allergens up to early adulthood by 29% (overall aOR = 0.71; 95% CI: 0.52-0.98), and to food allergens specifically by 40% (overall aOR = 0.60; 95% CI: 0.38-0.93). No relation was found between post-term birth and IgE sensitization at any time point. Replication analyses in STOPPA (N = 675) showed similar risk estimates for sensitization to food and/or inhalant allergens (aOR = 0.72; 95% CI: 0.42-1.21), which resulted in a combined meta-analysis aOR = 0.71 (95% CI: 0.54-0.94).

Conclusions: Our study suggests an inverse association between preterm birth and long-term IgE sensitization.