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Prevalence of Survival Without Major Comorbidities Among Adults Born Prematurely

Educational Objective
To understand the health challenges of adults who were born preterm.
1 Credit CME
Key Points

Question  What is the prevalence of survival without major comorbidities in adulthood among persons born prematurely?

Findings  In this population-based cohort study of more than 2.5 million persons born in Sweden from 1973 to 1997, 54.6% of those born preterm (gestational age <37 weeks) and 22.3% of those born extremely preterm (22-27 weeks) were alive with no major comorbidities at ages 18 to 43 years, compared with 63.0% of those born full-term. The prevalences were statistically significantly lower in those born at earlier gestational ages vs full-term.

Meaning  Among Swedish persons born prematurely, a large percentage survived into adulthood and had no major comorbidities.


Importance  Preterm birth has been associated with cardiometabolic, respiratory, and neuropsychiatric disorders in adulthood. However, the prevalence of survival without any major comorbidities is unknown.

Objective  To determine the prevalence of survival without major comorbidities in adulthood among persons born preterm vs full-term.

Design, Setting, and Participants  National cohort study of all 2 566 699 persons born in Sweden from January 1, 1973, through December 31, 1997, who had gestational age data and who were followed up for survival and comorbidities through December 31, 2015 (ages 18-43 years).

Exposures  Gestational age at birth.

Main Outcomes and Measures  Survival without major comorbidities among persons born extremely preterm (22-27 weeks), very preterm (28-33 weeks), late preterm (34-36 weeks), or early term (37-38 weeks), compared with full-term (39-41 weeks). Comorbidities were defined using the Adolescent and Young Adult Health Outcomes and Patient Experience (AYA HOPE) Comorbidity Index, which includes conditions that commonly manifest in adolescence or young adulthood, including neuropsychiatric disorders; and the Charlson Comorbidity Index (CCI), which includes major chronic disorders predictive of mortality in adulthood. Poisson regression was used to determine prevalence ratios and differences, adjusted for potential confounders.

Results  In this study population, 48.6% were female, 5.8% were born preterm, and the median age at end of follow-up was 29.8 years (interquartile range, 12.6 years). Of all persons born preterm, 54.6% were alive with no AYA HOPE comorbidities at the end of follow-up. Further stratified, this prevalence was 22.3% for those born extremely preterm, 48.5% for very preterm, 58.0% for late preterm, 61.2% for early term, and 63.0% for full-term. These prevalences were significantly lower for earlier gestational ages vs full-term (eg, adjusted prevalence ratios: extremely preterm, 0.35 [95% CI, 0.33 to 0.36; P < .001]; all preterm, 0.86 [95% CI, 0.85 to 0.86; P < .001]; adjusted prevalence differences: extremely preterm, −0.41 [95% CI, −0.42 to −0.40; P < .001]; all preterm, −0.09 [95% CI, −0.09 to −0.09; P < .001]). Using the CCI, the corresponding prevalences were 73.1% (all preterm), 32.5% (extremely preterm), 66.4% (very preterm), 77.1% (late preterm), 80.4% (early term), and 81.8% (full-term) (adjusted prevalence ratios: extremely preterm, 0.39 [95% CI, 0.38 to 0.41; P < .001]; all preterm, 0.89 [95% CI, 0.89 to 0.89; P < .001]; adjusted prevalence differences: extremely preterm, −0.50 [95% CI, −0.51 to −0.49; P < .001]; all preterm, −0.09 [95% CI, −0.09 to −0.09; P < .001]).

Conclusions and Relevance  Among persons born preterm in Sweden between 1973 and 1997, the majority survived to early to mid-adulthood without major comorbidities. However, outcomes were worse for those born extremely preterm.

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Article Information

Corresponding Author: Casey Crump, MD, PhD, Icahn School of Medicine at Mount Sinai, Departments of Family Medicine and Community Health and of Population Health Science and Policy, One Gustave L. Levy Place, Box 1077, New York, NY 10029 (

Accepted for Publication: August 28, 2019.

Author Contributions: Dr Jan Sundquist had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Concept and design: Crump, Winkleby, J. Sundquist.

Acquisition, analysis, or interpretation of data: All authors.

Drafting of the manuscript: Crump, Winkleby.

Critical revision of the manuscript for important intellectual content: All authors.

Statistical analysis: Crump, Winkleby.

Obtained funding: All authors.

Administrative, technical, or material support: Crump, J. Sundquist, K. Sundquist.

Supervision: Crump, K. Sundquist.

Conflict of Interest Disclosures: Dr Crump and Dr K. Sundquist reported receiving grants from the National Heart, Lung, and Blood Institute (NHLBI) during the conduct of the study. No other disclosures were reported.

Funding/Support: This work was supported by the NHLBI at the National Institutes of Health (R01 HL139536 to Drs Crump and K. Sundquist); the Swedish Research Council; the Swedish Heart-Lung Foundation; and Agreement on Medical Training and Research (ALF) project grant, Region Skåne/Lund University, Sweden.

Role of the Funder/Sponsor: The sponsors/funders had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

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