Risk of warfarin during pregnancy with mechanical valve prostheses

OBJECTIVE: To assess the determinants of pregnancy outcome in patients with mechanical valve prostheses anticoagulated with warfarin. METHODS: Between January 1987 and January 2000, 52 patients with mechanical valve prostheses who had 71 pregnancies were anticoagulated with warfarin for the entire duration of pregnancy. Warfarin was withdrawn 48 hours before and 24 hours after a scheduled cesarean delivery carried out by the end of the 37th gestational week. The targeted international normalized ratio ranged between 2.25 and 4.0, depending on the prosthetic model. Exact univariate and multivariable analyses were performed to assess which among the following variables predicted poor pregnancy outcome: patient age, prosthetic model, site of implantation, average international normalized ratio, and average daily dose of warfarin. RESULTS: Pregnancy loss occurred in 23 of 71 of pregnancies, stillbirth in five of 71, embryopathy in four of 71 (two aborted fetuses and two full-term infants). There were no maternal deaths or thromboembolic or hemorrhagic complications. Warfarin daily dosage over 5 mg per day was a significant predictor of poor pregnancy outcome (P <.001). CONCLUSION: The risk for pregnancy complications in patients treated with sodium warfarin is higher when the mean daily dose exceeds 5 mg.