Changes in the plasma activities of protein C and protein S during pregnancy

The objective of the study was to determine the changes in the plasma activ ities of protein C and protein S that occur during normal pregnancy. In thi s prospective cross-sectional study, plasma activities of protein C and pro tein S were measured in 32 normal pregnant women in the first, second and t hird trimester and 6 weeks after delivery; There was a significant fall in protein C and protein S activities during normal pregnancy compared with th e post-puerperal period. The activities of protein C and protein S also gra dually decreased throughout pregnancy (p < 0.01). Increasing plasma volume during normal pregnancy and its dilutional effect might play some role in t he low activities of protein S observed. The normal falls in protein S and protein C activities make it difficult to diagnose protein S and C deficien cy during pregnancy. Based on our findings, if a woman has a thromboembolic event during pregnancy; testing for a definitive diagnosis of protein C or protein S deficiency or functional failure should be delayed until at leas t 6 weeks postpartum.