Response to activated protein C decreases throughout pregnancy

Background. The possibility that changes in activated protein C anticoagulant activity may contribute to the hemostatic changes associated with pregnancy has been previously investigated, but the results of the studies are still controversial. Methods. Nine hundred and sixty-one healthy nonpregnant and 711 normal pregnant women who were noncarriers of factor V Leiden at different weeks' gestation were included in a cross-sectional trial. Moreover, the APC ratio was repeatedly measured in 45 women throughout pregnancy. The activated protein C ratio was tested using the modified activated partial thromboplastin time-based assay. Results. A significantly lower APC ratio was observed at 20-28 and 32-38 (p = 0.0001) weeks' gestation compared with nonpregnant values. The decrease in the APC ratio throughout pregnancy showed a significant trend (p = 0.014). In none of the subjects did the APC ratio reach the cut-off values for APC resistance. Conclusions. Our data confirm a reduction in the APC ratio throughout pregnancy. In our series, an APC ratio of less than 2.0 according to the cut-off point of our laboratory).