OBJECTIVE. Increasing numbers of infants born preterm survive into adulthood. Previous studies have reported increased levels of neurologic and cognitive disabilities in these children. In this study, we analyzed the effect of having been born preterm on psychiatric morbidity.

METHODS. A Swedish national cohort of 545628 individuals born in 1973–1979 was followed up in the national registers during 1987–2002. Multivariate Cox analysis of proportional hazards was used to estimate the hazard ratios of hospital admissions for psychiatric disorders and alcohol/illicit drug abuse.

RESULTS. There was a stepwise increase in psychiatric hospital admissions with an increasing degree of preterm birth. A total of 5.2% of children born at 24 to 28 weeks’ gestation and 3.5% born at 29 to 32 weeks’ gestation had been hospitalized because of a psychiatric disorder. The hazard ratios for psychiatric disorders were 1.68 in the group of very preterm children (gestational weeks 24–32), 1.21 in the moderately preterm group (gestational weeks 33–36), and 1.08 in the early term group (gestational weeks 37–38) after adjustment for socioeconomic confounders. Moderately preterm and early term birth accounted for 85% of the risk attributed to preterm/early term birth. The effect of preterm birth was greater in households with low socioeconomic status.

CONCLUSION. Preterm birth carries some risk for psychiatric disorders requiring hospitalization in adolescence and young adulthood (ages 8–29 years). Even if this risk increases with degree of preterm birth, most subjects are moderately preterm, a group in need of more attention in research and secondary prevention.

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