Increased risk for fetal loss in carriers of the factor V Leiden mutation.

BACKGROUND: An increased risk for fetal loss caused by placental thrombosis is probable in carriers of the factor V Leiden mutation but has not been demonstrated consistently in previous studies. OBJECTIVE: To determine the overall risk for fetal loss and the separate risks for miscarriage and stillbirth in carriers of the factor V Leiden mutation. DESIGN: Retrospective cohort study. SETTING: Three university hospitals. PARTICIPANTS: 228 carriers of the factor V Leiden mutation (77 propositi, 151 relatives) and 121 noncarrier relatives (controls). All participants had been pregnant at least once. MEASUREMENTS: Risks for fetal loss, miscarriage (defined as fetal loss within 20 weeks of gestation), and stillbirth (defined as fetal loss after >20 weeks of gestation) in women and in pregnancies were estimated and compared in carriers and noncarriers. Adjusted odds ratios were calculated by using multiple regression analysis. A random-effects model was used for comparisons of pregnancies. RESULTS: Fetal loss occurred in 31.6% of carriers and 22.3% of noncarriers, miscarriage occurred in 29.4% of carriers and 17.4% of noncarriers, and stillbirth occurred in 5.7% of carriers and 5.0% of noncarriers. Fetal loss recurred in 10.1% of carriers and 4.1% of noncarriers (odds ratio, 2.60 [95% CI, 0.96 to 7.03]). Adjusted odds ratios were 2.12 (CI, 1.35 to 3.33) for fetal loss, 2.08 (CI, 1.33 to 3.25) for miscarriage, and 1.60 (CI, 0.58 to 4.43) for still-birth when pregnancies in carriers and noncarriers were compared. Homozygous carriers had a greater risk for fetal loss (odds ratio, 2.01 [CI, 0.94 to 4.32]) and stillbirth (odds ratio, 4.85 [CI, 0.82 to 25.58]) than heterozygous carriers. CONCLUSIONS: Carriers of the factor V Leiden mutation have a greater risk for fetal loss (particularly miscarriage) than noncarriers. These data further suggest a greater risk for recurrence of fetal loss in carriers than in noncarriers and a greater risk for fetal loss and stillbirth in homozygous carriers than in heterozygous carriers.