Thromboembolism and in vitro fertilization - a systematic review.

INTRODUCTION: There is no accepted consensus on thromboprophylaxis in relation to in vitro fertilization (IVF). We aimed to study the frequency of thromboembolism and to assess thromboprophylaxis in relation to IVF.

MATERIAL AND METHODS: We performed a systematic review. All study designs were accepted except single case reports. Language of included articles was restricted to English.

RESULTS: Of 338 articles, 21 relevant articles (nine cohort studies, six case-control studies, three case series, and three reviews of case series) were identified. The antepartum risk of venous thromboembolism (VTE) after IVF is doubled (odds ratio 2.18, 95% CI 1.63-2.92), compared with the background pregnant population. This is due to a 5- to 10-fold increased risk during the first trimester in IVF pregnancies, in turn related to a very high risk of VTE after ovarian hyperstimulation syndrome (OHSS), i.e. up to a 100-fold increase, or an absolute risk of 1.7%. The interval from embryo transfer to VTE was 3-112 days and the interval from embryo transfer to arterial thromboembolism was 3-28 days. No robust study on thromboprophylaxis was found.

CONCLUSIONS: The antepartum risk of VTE after IVF is doubled, compared with the background pregnant population, and is in turn related to a very high risk of VTE after OHSS in the first trimester. We recommend that IVF patients with OHSS be prescribed low-molecular-weight heparin during the first trimester, whereas other IVF patients should be given thromboprophylaxis based on the same risk factors as other pregnant women.