Factor V Leiden mutation in relation to fecundity and miscarriage in women with venous thrombosis

Factor V Leiden mutation (Arg506Gln) increases the likelihood of venous thrombosis; it may also have a positive effect through facilitation of embryo implantation. This may manifest itself as a reduced time to pregnancy (increased fecundity) and fewer miscarriages in the first trimester.From March 1999 onwards, consecutive patients with a first venous thrombosis (VT) were recruited. The first 115 female VT patients with factor V Leiden and 230 age-matched female VT patients without factor V Leiden were included. All patients, unaware of their genotype, received a structured questionnaire.Of the 297 (86%) women who returned the questionnaire, 220 had been pregnant at least once. Time to first pregnancy was unaffected by carrier status: 58% factor V Leiden carriers reported a pregnancy within 3 months compared to 54% non-carriers. The miscarriage proportion was 14%, similar in both groups. First trimester miscarriage was less frequent among carriers (46%) than among non-carriers (95%) (relative risk 0.5, 95% confidence interval 0.3-0.9).Factor V Leiden mutation may support embryo implantation, as factor V Leiden carriers had fewer miscarriages in the first trimester with a similar overall miscarriage rate. Miscarriage of embryos with poor viability may be postponed until the second trimester in factor V Leiden carriers. Fecundity was not influenced by factor V Leiden status.