Relationship between maternal antithrombin III and protein C/protein S levels before, during and after delivery

The relationship between plasma levels of protein C, protein S and antithrombin III was examined in a group of normal pregnant Chinese women with singleton pregnancies to study the changes in the anticoagulant system in relation to pregnancy, labour and the puerperium. A significant correlation was found between protein C and antithrombin III both before labour and postpartum, and the ratio was close to unity. When the two groups are combined, a highly significant correlation was found (r = 0.758; p less than 0.001). The correlation is not observed at delivery when the ratio becomes very variable and in general greater than unity. The correlation between protein S and antithrombin III was 0.592 before labour and -0.532 at delivery, but both failed to reach statistical significance because of the small numbers. When postpartum concentration of protein C, protein S and antithrombin III is related to interval between sampling and delivery, significant correlation was found only with protein S. The results of this study suggest that the plasma level of protein C and probably protein S is correlated with that of antithrombin III during pregnancy, labour and the puerperium.