Preterm delivery and long term mortality in women: national cohort and co-sibling study [女性早产与远期病死率：国家队列与同胞研究]

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BMJ 2020; 370 doi: https://doi.org/10.1136/bmj.m2533 (Published 19 August 2020)
Cite this as: BMJ 2020;370:m2533

Authors
Casey Crump, Jan Sundquist, Kristina Sundquist

Abstract
Objectives To examine the long term mortality associated with preterm delivery in a large population based cohort of women, and to assess for potential confounding by shared familial factors.

Design National cohort study.

Setting Sweden.

Participants All 2 189 477 women with a singleton delivery in 1973-2015.

Main outcome measures All cause and cause specific mortality up to 2016, identified from nationwide death records. Cox regression was used to calculate hazard ratios while adjusting for confounders, and co-sibling analyses assessed the potential influence of unmeasured shared familial (genetic and environmental) factors.

Results In 50.7 million person years of follow-up, 76 535 (3.5%) women died (median age at death was 57.6). In the 10 years after delivery, the adjusted hazard ratio for all cause mortality associated with preterm delivery (<37 weeks) was 1.73 (95% confidence interval 1.61 to 1.87), and when further stratified was 2.20 (1.63 to 2.96) for extremely preterm delivery (22-27 weeks), 2.28 (2.01 to 2.58) for very preterm delivery (28-33 weeks), 1.52 (1.39 to 1.67) for late preterm delivery (34-36 weeks), and 1.19 (1.12 to 1.27) for early term delivery (37-38 weeks) compared with full term delivery (39-41 weeks). These risks declined but remained significantly raised after longer follow-up times: for preterm versusfull term births, 10-19 years after delivery, the adjusted hazard ratio was 1.45 (95% confidence interval 1.37 to 1.53); 20-44 years after delivery, the adjusted hazard ratio was 1.37 (1.33 to 1.41). These findings did not seem to be attributable to shared genetic or environmental factors within families. Several causes were identified, including cardiovascular and respiratory disorders, diabetes, and cancer.

Conclusions In this large national cohort of women, the findings suggested that preterm and early term delivery were independent risk factors for premature mortality from several major causes. These associations declined over time but remained raised up to 40 years later.