Summary Total and free protein S antigen and C4b-binding protein (C4bp) were determined by rocket immuno-electrophoresis, and functional protein S was assayed by a coagulation method, throughout pregnancy and normal puerperium and in a group of normal full-term newborns (FTN). The functional protein S assay is based on a modification of the APTT, using a mixture of test sample, protein S deficient plasma, activated protein C, phospholipids and calcium. This protein S functional assay is specific for protein S since the APTT prolongation by normal plasma was abolished by incubation of plasma with monospecific, rabbit antiprotein S IgG. The ratios of functional protein S/free protein S antigen in healthy men (n = 13) and women (n = 14) were 1.0 ± 0.13 (mean ± SD) and 1.03 ± 0.20, respectively. During pregnancy there is a decrease in functional protein S and a progressive decrease in total and free protein S antigen, with a functional/free protein S ratio of 0.75 ± 0.28 in the third trimester of pregnancy (n = 16). In early puerperium the functional protein S level was lower than the free protein S antigen level (ratio about 0.5). In the FTN group, the free protein S level was 39% and protein S activity was about 70% that of adults, with a functional/free protein S ratio of 1.84 ± 0.31. C4bp values were 23.5 ± 10.3% in the FTN group, and crossed immunoelectrophoresis showed that in this group the major protein S peak corresponded to free protein S. These results indicate that both in early puerperium and in FTN group, free protein S antigen may not be an adequate parameter for estimating of functional protein S activity. The decrease in functional protein S activity during early puerperium may be connected with the risk of developing thrombotic episodes during the postpartum period.
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Fernández et al. (1989) studied this question.