Venous thromboembolism in relation to in vitro fertilization: an approach to determining the incidence and increase in risk in successful cycles

ObjectiveTo determine the incidence and the increase in risk of venous thromboembolism (VTE) in relation to IVF and ovarian hyperstimulation syndrome (OHSS) in successful cycles.DesignCohort study.SettingPopulation based.Patient(s)All deliveries (n = 964,532) in Sweden during a 10-year period (1999–2008).Intervention(s)Comparison of VTEs among those with and without IVF. The National Birth Registry was cross-matched with both the National Discharge Registry and the National IVF Registry. Logistic regression analysis was used to determine odds ratios and 95% confidence intervals.Main Outcome Measure(s)Risk of first trimester VTE.Result(s)The incidence of first-trimester VTE in relation to IVF was 0.2%, representing a 10-fold increase as compared with the background population. The 6% to 7% of IVF pregnancies that were complicated by OHSS showed a 100-fold increased risk of VTE, as opposed to the fivefold increased risk seen in the absence of OHSS. The VTEs in conjunction with IVF were diagnosed at a mean gestational age of 62 days; there was no increased risk of VTE related to frozen embryo replacement cycles or IVF after the first trimester.Conclusion(s)Treating women with OHSS with low-molecular-weight heparin thromboprophylaxis during the first trimester and treating cases at high-risk for OHSS with frozen embryo replacement is likely to lower the risk of VTE.