Context: Preterm birth is a major cause of infant morbidity and mortality. Less is known about long-term health among persons born preterm.
Objective: To determine the long-term effects of preterm birth on survival, reproduction, and next-generation preterm birth.
Design, setting, and participants: Population-based, observational, longitudinal study using registry data from 1,167,506 singleton births in the Medical Birth Registry of Norway in 1967-1988. The cohort was followed up through 2002 for survival. The cohort was truncated to births from 1967-1976 for assessment of educational achievement and reproductive outcomes through 2004.
Main outcome measures: In relation to sex and gestational age at birth, absolute mortality, risk of fetal, infant, child, and adolescent mortality, and incidence and risk of reproduction and next-generation preterm birth. Singleton term (37-42 weeks) fetal deaths and live births, stratified by sex, served as the reference group for all analyses.
Results: The percentage who were born preterm was higher among boys (5.6%) than among girls (4.7%). Preterm participants had an increased risk of mortality throughout childhood. For boys born at 22 to 27 weeks, mortality rates were 1.33% and 1.01% for early and late childhood death, with relative risks (RRs) of 5.3 (95% confidence interval [CI], 2.0-14.2) and 7.0 (95% CI, 2.3-22.0), respectively. The mortality rate for girls born at 22 to 27 weeks was 1.71% for early childhood death, with an RR of 9.7 (95% CI, 4.0-23.7); there were no late childhood deaths. For 28 to 32 weeks, the early and late childhood mortality rates among boys were 0.73% and 0.37%, with RRs of 2.5 (95% CI, 1.6-3.7) and 2.3 (95% CI, 1.3-4.1), respectively. Girls born at 28 to 32 weeks did not have a significantly increased risk of childhood mortality. Reproduction was diminished for index participants born preterm. For men and women born at 22 to 27 weeks, absolute reproduction was 29.3[corrected]% and 51.9[corrected]%, with RRs of 0.59 [corrected] (95% CI, 0.45[corrected]-0.79[corrected]) and 0.78 [corrected] (95% CI, 0.65[corrected]-0.93[corrected]), respectively. For 28 to 32 weeks, absolute reproduction was 43.1[corrected]% and 63.6[corrected]% for men and women, with RRs of 0.81[corrected] (95% CI, 0.77[corrected]-0.86[corrected]) and 0.89 [corrected] (95% CI, 0.86 [corrected]-0.93 [corrected]), respectively. Preterm women but not men were at increased risk of having preterm offspring.
Conclusion: In persons born in Norway in 1967-1988, preterm birth was associated with diminished long-term survival and reproduction.