Combined hormonal contraception and risk of venous thromboembolism within the first year following pregnancy

Abstract

Estimating the risk of venous thromboembolism (VTE) associated with combined hormonal contraceptives following early terminated pregnancies or birth, a Danish nationwide retrospective cohort observing a one-year follow-up was defined using three unique registries. All Danish women with confirmed pregnancies aged 15-49 during the period of 1995-2009 were included. The main outcomes were relative and absolute risks of first time venous thromboembolism in users as well as non-users of combined hormonal contraceptives. In 985,569 person-years, 598 venous thromboembolisms were recorded. After early terminated pregnancies and births, respectively, 113 and 485 events occurred in 212,552 and 773,017 person-years. After early terminated pregnancies, the crude VTE incidence ratios were similar, and the numbers needed to harm were equal between groups that did or did not use combined hormonal contraceptives throughout the follow-up year. After childbirth, individuals that used combined hormonal contraceptives were more likely than non-users to experience VTE depicted by crude incidence ratios; however, the difference was only significant after 14 weeks. This implied that the numbers needed to harm were lower for those that used compared to those that did not use combined oral contraceptives in the initial 14 weeks postpartum. In conclusion, the use of combined hormonal contraceptives after early terminated pregnancies was not detrimental, but during the puerperal period, they should be used with caution.