OBJECTIVE: A common missense mutation in the factor V gene, the Leiden mutation, renders factor Va resistant to cleavage inactivation by activated protein C and predisposes patients to thrombotic events. We sought to evaluate the prevalence of the Leiden mutation and the associated thromboembolic events in a community hospital's low-risk obstetric population.

STUDY DESIGN: Deoxyribonucleic acid was extracted from whole blood of 407 women. The polymerase chain reaction was used to amplify exon 10 of the factor V gene, followed by enzymatic digestion with Mnl 1 for mutation detection. Medical charts were reviewed and patient characteristics, including age, gravidity, parity, obstetric complications, medical complications, and mode of delivery, were recorded.

RESULTS: Fourteen of the 407 women carried the factor V Leiden mutation (13 heterozygotes and 1 homozygous mutant) for an allele frequency of 3%, consistent with the published carrier rate. Four of the 14 carriers (28%) had deep venous thrombosis, whereas the frequency of deep venous thrombosis in this obstetric population was <1%. Another patient carrying the mutation had a consumptive coagulopathy of unknown etiology at 20 weeks' gestation, necessitating delivery.

CONCLUSIONS: The Leiden mutation is relatively common in the general obstetric population. The high rate of deep venous thrombosis noted in our series suggests the need for genetic testing for this mutation in women with a thrombotic event during pregnancy. (Am J Obstet Gynecol 1997;176:883-6.)