Individual risk assessment of thrombosis in pregnancy.

Thromboembolic complications during pregnancy are major contributors to maternal death, but there is no reliable way to estimate the absolute risk of thrombosis before the occurrence of a thromboembolic complication. OBJECTIVE: To create a model for individual estimation of thrombosis risk during pregnancy and to determine the distribution of risk estimates in a series of gravidae. METHOD AND PATIENTS: Estimates of absolute risk of pregnancy-related thromboembolism were calculated by multiplying reported figures of thrombosis incidence by prevalence-adjusted odds ratios of the following variables: smoking, parity, preeclampsia, mode of delivery, age, overweight, activated protein C resistance (FV Leiden or FV:Q506), thrombosis heredity, and previous thrombosis. We present the risk distribution among a unselected prospectively gathered cohort of 2384 unselected gravidae who were interviewed and tested for activated protein C resistance in early pregnancy. RESULTS AND CONCLUSIONS: A model for individual estimation of the absolute risk of thrombosis is presented, which is provided to the readers as a free automatic Internet-based service (http://www.riskpreg.com). As compared with antepartum, more women at high risk can be identified in the postpartum period and we suggest that this might be of use in planning the prevention of thrombosis.