Hospital admissions for lower respiratory tract infections after early-, late-, and post-term birth.

Background: Recent data suggest that early-term births are associated with later respiratory morbidity (LRTI), and post-term births may decrease this risk.

Objectives: The objective was to determine the impact of early-term, late-term, and post-term birth on hospital admission for LRTI up to the age of seven years. Additionally, we explored maternal and perinatal factors associated with the risk of admission for LRTIs.

Methods: The association of early-term (37 -38  weeks), late-term (41 -41  weeks), and post-term (≥42 weeks) birth with hospital admissions for lower respiratory tract infections (LRTI) in comparison with infants born full-term (39 -40  weeks) was assessed and early predictors of LRTI were established. The register study included 948 695 infants born in Finland in 1991-2008. Data were analysed in four-term subgroups. Hospital admissions for bronchiolitis/bronchitis and pneumonia were collected up to 7 years of age. Adjusted Cox proportional hazards models were used to assess risk factors of LRTI admissions.

Results: The rates of hospital admission in the early-, full-, late-, and post-term groups were 6.7%, 5.5%, 5.1%, and 4.8% for bronchiolitis/bronchitis, and 2.8%, 2.4%, 2.3%, and 2.3% for pneumonia. Early-term birth was associated with an increased risk of admission for bronchiolitis/bronchitis (hazard ratio HR 1.21, 95% confidence interval CI 1.18, 1.23) and pneumonia (HR 1.16, 95% CI 1.12, 1.20), while late-term (HR 0.93, 95% CI 0.91, 0.95) and post-term births (HR 0.89, 95% CI 0.85, 0.93) were associated with a decreased risk of bronchiolitis/bronchitis admission compared with the full-term group. Maternal age ≤ 20 years, smoking during pregnancy, male sex, caesarean delivery, small for gestational age, 1-minute Apgar score < 4, ventilator support, and neonatal antibiotic therapy were associated with an increased risk of LRTI admission, while being firstborn, born in a level-II hospital and in the Northern region was associated with decreased risk.

Conclusion: Early-term birth was associated with a higher risk of all LRTI admissions while late-term and post-term births were associated with lower risk of bronchiolitis/bronchitis admission. Modifiable risk factors of LRTIs were smoking during pregnancy, birth by elective caesarean delivery, neonatal ventilator support, and antibiotic therapy.