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

OBJECTIVE: To determine the incidence and the increase in risk of venous thromboembolism (VTE) in relation to IVF and ovarian hyperstimulation syndrome (OHSS) in successful cycles.

DESIGN: Cohort study.

SETTING: Population 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.