Premature Adult Death in Individuals Born Preterm: A Sibling Comparison in a Prospective Nationwide Follow-Up Study.
BACKGROUND
Close to one in ten individuals worldwide is born preterm, and it is important to understand patterns of long-term health and mortality in this group. This study assesses the relationship between gestational age at birth and early adult mortality both in a nationwide population and within sibships. The study adds to existing knowledge by addressing selected causes of death and by assessing the role of genetic and environmental factors shared by siblings.


METHODS
Study population was all Norwegian men and women born from 1967 to 1997 followed using nation-wide registry linkage for mortality through 2011 when they were between 15 and 45 years of age. Analyses were performed within maternal sibships to reduce variation in unobserved genetic and environmental factors shared by siblings. Specific outcomes were all-cause mortality and mortality from cardiovascular diseases, cancer and external causes including accidents, suicides and drug abuse/overdoses.


RESULTS
Compared with a sibling born in week 37-41, preterm siblings born before 34 weeks gestation had 50% increased mortality from all causes (adjusted Hazard Ratio (aHR) 1.54, 95% confidence interval (CI) 1.17, 2.03). The corresponding estimate for the entire population was 1.27 (95% CI 1.09, 1.47). The majority of deaths (65%) were from external causes and the corresponding risk estimates for these deaths were 1.52 (95% CI 1.08, 2.14) in the sibships and 1.20 (95% CI 1.01, 1.43) in the population.


CONCLUSIONS
Preterm birth before week 34 was associated with increased mortality between 15 and 45 years of age. The results suggest that increased premature adult mortality in this group is related to external causes of death and that the increased risks are unlikely to be explained by factors shared by siblings.
Department of Pediatrics, St Olav Hospital, University Hospital, Trondheim, Norway.|Institute of Public Health and General Practice, NTNU, Norwegian University of Science and Technology, Trondheim, Norway.
Kari R
KR
Risnes
Institute of Public Health and General Practice, NTNU, Norwegian University of Science and Technology, Trondheim, Norway.
Kristine
K
Pape
Institute of Public Health and General Practice, NTNU, Norwegian University of Science and Technology, Trondheim, Norway.|Forensic Department and Research Centre Bröset St. Olav's University Hospital, Trondheim, Norway.
Johan H
JH
Bjørngaard
Department of Global Public Health and Primary Care, University of Bergen, Bergen, Norway.|Department of Pediatrics, Haukeland University Hospital, Bergen, Norway.|Norwegian Institute of Public Health, Oslo, Norway.
Dag
D
Moster
Schools of Public Health and Medicine, Yale University, New Haven, Connecticut, United States of America.
Michael B
MB
Bracken
Institute of Public Health and General Practice, NTNU, Norwegian University of Science and Technology, Trondheim, Norway.
Pal R
PR
Romundstad
D000293:Adolescent; D015331:Cohort Studies; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D061213:Mortality, Premature; D047928:Premature Birth; D011446:Prospective Studies; D035781:Siblings; D055815:Young Adult