Evaluation of the plasma protein S dynamics during pregnancy using a total protein S assay: Protein S-specific activity decreased from the second trimester.

Abstract

The relationship between congenital protein S (PS) deficiency and complications during pregnancy remains unclear, partly due to the difficulty of precisely evaluating the PS level with conventional assays and the physiological decrease of PS during pregnancy. A new PS assay was developed to measure the total PS antigen and activity quantitatively and calculate PS-specific activity. This study aimed to evaluate the plasma PS dynamics during pregnancy using the new PS assay and establish the reference interval for pregnant women. A total of 253 pregnant women without a personal or family history of thromboembolism were recruited. Blood samples were obtained in the first, second and third trimesters and at one month post-partum. The total PS antigen, activity, and PS-specific activity were studied. Results were analyzed by the repeated measures single-factor anovas followed by a post-hoc test using Excel Statistics. The mean ± standard deviation (IU/mL) of the total PS antigen levels in the first, second and third trimesters and 1 month post-partum were 0.67 ± 0.12, 0.67 ± 0.09, 0.68 ± 0.11 and 0.92 ± 0.13, respectively. The total PS activity (IU/mL) in the first, second and third trimesters and 1 month post-partum were 0.69 ± 0.14, 0.59 ± 0.10, 0.58 ± 0.12 and 0.87 ± 0.15, respectively. The PS-specific activity was within the normal range of nonpregnant women in the first trimester (1.02 ± 0.10) but decreased in the second and third trimesters (0.88 ± 0.09 and 0.85 ± 0.09, respectively) before increasing in the post-partum period (0.94 ± 0.08). The total PS antigen and activity decrease throughout pregnancy, while the PS-specific activity decreases in the second and third trimesters.