Gestational age and risk of venous thromboembolism from birth through young adulthood

Preterm birth has been associated with increased risk of venous thromboembolism (VTE) in infancy, but the longer-term risk is unknown. Our aim was to examine this association from birth through young adulthood.

National cohort study of 3,571,574 individuals who were live-born in Sweden from 1973 through 2008, including 206,844 born preterm (gestational age <37 weeks), and followed up to 2010 (ages 0-38 years). The main outcome was VTE.

A total of 7519 (0.2%) individuals were diagnosed with VTE in 70.8 million person-years of follow-up. Low gestational age at birth was associated with VTE in infancy (ages <1 year: adjusted hazard ratio 47.16 [95% confidence interval 21.30-104.42] for 22 to 27 weeks, 5.54 [2.53-12.12] for 28 to 33 weeks, 3.54 [2.07-6.06] for 34 to 36 weeks, 1.00 for 37 to 41 weeks [reference]), early childhood (ages 1-5 years), and young adulthood (ages 18-38 years: adjusted hazard ratio 2.76 [1.43-5.31] for 22 to 27 weeks, 1.53 [1.24-1.89] for 28 to 33 weeks, 1.24 [1.10-1.40] for 34 to 36 weeks, and 1.00 for 37 to 41 weeks [reference]), but not in late childhood (ages 6-12 years). Very preterm (<34 weeks) but not late preterm birth (34-36 weeks) was also associated with VTE in adolescence (ages 13-17 years). After further adjustment for comorbidities, these associations were attenuated, but most remained significantly elevated.

In this large national cohort, low gestational age at birth was associated with increased risk of VTE in infancy, early childhood, and young adulthood.