Risk factors for first venous thromboembolism around pregnancy: a population based cohort study from the United Kingdom

Alyshah Abdul Sultan, Laila J. Tata, Joe West, Linda Fiaschi, Kate M. Fleming, Catherine Nelson-Piercy and Matthew J. Grainge

Key points

  • Antepartum, we found that established risk factors only had a modest effect on rates of VTE.

  • Postpartum, we found that among other factors, women with stillbirth or pre-term birth had high rates of VTE.


Knowledge of the absolute risk (AR) of venous thromboembolism (VTE) in women around pregnancy and how potential risk factors modify this risk is crucial in identifying women who would benefit most from thromboprophylaxis. We addressed this using a large primary care database containing 376,154 pregnancies ending in live birth or stillbirth from women aged 15-44 years between 1995 and 2009. We assessed the impact of risk factors on the incidence of antepartum and postpartum VTE in terms of ARs and incidence rate ratios (IRR) using Poisson regression. During antepartum, varicose veins, inflammatory bowel disease (IBD), urinary tract infection and pre-existing diabetes were associated with an increased risk of VTE (ARs≥139/100,000 person-year; IRRs≥1.8). Postpartum, the strongest risk factor was stillbirth (AR=2,444/100,000 person-years; IRR=6.2) followed by medical co-morbidities (including varicose veins, IBD or cardiac disease), BMI≥30kg/m2, obstetric haemorrhage, preterm delivery, and caesarean section (ARs≥637/100,000 person-years; IRRs≥1.9). Our findings suggest that VTE risk varies modestly by recognised factors during antepartum, however women with stillbirths, preterm births, obstetric haemorrhage, caesarean section delivery, medical co-morbidities or BMI≥30kg/m2 are at much higher risk of VTE following delivery. These risk factors should receive careful consideration when assessing the potential need for thromboprophylaxis during the postpartum period.

  • Submitted November 26, 2012.
  • Accepted February 27, 2013.