Association of preterm birth with long-term survival, reproduction, and next-generation preterm birth

Preterm birth is a major cause of infant morbidity and mortality. Less is known about long-term health among persons born preterm.

To determine the long-term effects of preterm birth on survival, reproduction, and next-generation preterm birth.

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.

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.

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.

In persons born in Norway in 1967-1988, preterm birth was associated with diminished long-term survival and reproduction.