Gestational age, birth weight, and risk of respiratory hospital admission in childhood.

OBJECTIVE: To investigate the risk of emergency respiratory hospital admission during childhood associated with gestational age at birth and growth restriction in utero.
METHODS: The study included a total population electronic birth cohort with anonymized record-linkage of multiple health and administrative data sets. Participants were 318,613 children born in Wales, United Kingdom, between May 1, 1998, and December 31, 2008. The main outcome measure was emergency respiratory hospital admissions.
RESULTS: The rate of admission in the first year of life ranged from 41.5 per 100 child-years for infants born before 33 weeks' gestation to 9.8 per 100 child-years for infants born at 40 to 42 weeks' gestation. The risk of any emergency respiratory admission up to age 5 years increased as gestational age decreased to <40 weeks. Even at 39 weeks' gestation, there was an increased risk of emergency hospital admissions for respiratory conditions compared with infants born at 40 to 42 weeks (adjusted hazard ratio 1.10; 95% confidence interval 1.08-1.13). Small for gestational age (<10th centile for gestation and gender-specific birth weight) was independently associated with an increased risk of any emergency respiratory admission to hospital (adjusted hazard ratio 1.07; 95% confidence interval 1.04-1.10).
CONCLUSIONS: The risk of emergency respiratory admission up to age 5 years decreased with each successive week in gestation up to 40 to 42 weeks. Although the magnitude of increased risk associated with moderate and late preterm births is small, the number of infants affected is large and therefore presents a significant impact on health care services.