The risk of fetal loss in family members of probands with factor V Leiden mutation

In order to investigate the risk of fetal loss in carriers of factor V Leid en who are family members of probands with this mutation, we performed a re trospective cohort study including 109 women who had been pregnant at least once and were family members of 61 probands with venous thromboembolism an d a single identified factor V Leiden mutation. The rate of pregnancies end ing in unexplained fetal loss, early miscarriage, late miscarriage or still birth in women with the factor V Leiden was compared with that of women wit h normal genotype. In the 65 women who were carriers of factor V Leiden 31 of the 191 pregnancies (16.2% per pregnancy) resulted in unexplained fetal loss, as compared to 13 of the 121 pregnancies (10.7% per pregnancy) in the 44 non-carriers (relative risk, 1.5; 95% CI, 0.8-3.2). After the first tri mester of pregnancy, 25 pregnancies (13.1% per pregnancy) among carriers of factor V Leiden ended in fetal loss, as compared to 7 (5.8% per pregnancy) among females with normal genotype (relative risk, 2.3; 95% CI, 1.01 to 5. 1). We conclude that carriers of factor V Leiden who are family members of probands with this mutation have a statistically significant and clinically important risk of late miscarriage or stillbirth. Studies addressing the b enefit-to-risk ratio of adopting routinary thromboprophylactic measures fol lowing the first trimester of pregnancy in these women are strongly indicat ed.