Objective: Polymorphisms in the genes for factor V (factor V Leiden), prothrombin, methylenetetrahydrofolate reductase, and angiotensin-converting enzyme have been associated with the occurrence of venous thrombosis. The objective of this study was to determine the relationships of these polymorphisms to thrombosis during pregnancy. Study Design: This case-control study included 41 case patients with venous thrombosis during pregnancy and 76 control subjects matched for hospital and for race (white vs black) who had a normal pregnancy. Results: Among white subjects, mutations in the genes for factor V and prothrombin were associated with increased risks of venous thrombosis during pregnancy (factor V: odds ratio, 18.3; 95% confidence interval, 2.7-432; P =.001; prothrombin: odds ratio ∞; 95% lower confidence limit, 1.7; P =.01). No black subject had either of these two mutations. For both black and white subjects the D/D genotype of the gene for angiotensin-converting enzyme entailed increased risk compared with the other genotypes (odds ratio, 2.7; 95% confidence interval, 1.2-6.3; P =.02). The polymorphism in the gene for methylenetetrahydrofolate reductase was unrelated to thrombosis during pregnancy among both blacks and whites. Conclusion: Women who had thrombotic complications during pregnancy demonstrated an increased prevalence of genetic mutations related to coagulation. The additional risk of thrombosis during pregnancy associated with such genetic mutations can be substantial. (Am J Obstet Gynecol 2000;183:1271-7.)
