Heterozygote carriers of mutations in the F11 gene, encoding Factor XI, have normal coagulation by thromboelastography during pregnancy.

BACKGROUND: Evidence to guide clinical decision-making in pregnant women who are usually asymptomatic, but identified as heterozygote carriers of F11 mutations, is lacking. We hypothesized that women identified on prenatal screening as heterozygous for a mutation in the F11 allele would have minimal evidence of an in vitro coagulation abnormality.

METHODS: We prospectively enrolled women identified by prenatal screening as F11 mutation carriers and pregnant women who were presumed to be normal as controls. We collected blood during antepartum visits or at presentation for delivery and assessed Factor XI (FXI) coagulant activity level, as well as whole-blood coagulation, by thromboelastography.

RESULTS: F11 mutation carriers had lower serum FXI activity levels than controls (51.2 ± 8.5% vs 94.1 ± 19.4%; P <0.0001). Thromboelastography values of all control subjects and F11 mutation carriers were within the normal range. The R-time was slightly longer in F11 mutation carriers (5.3 ± 1.0 s vs 4.2 ± 0.8 s, P <0.002), but no other statistically significant differences in thromboelastogram parameters were identified between groups.

CONCLUSIONS: Despite lower FXI activity in the F11 mutation group, we found minimal differences in whole-blood measures of coagulation using thromboelastography. These findings support our hypothesis that a single copy of an F11 mutation does not produce significant evidence of an in vitro coagulation abnormality. Thromboelastography might be useful in determining the risk of neuraxial anesthesia in pregnant women, but additional work is required to establish the validity of this test.