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 Aim 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. Methods 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 anova s followed by a post‐hoc test using Excel Statistics. Results 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). Conclusion The total PS antigen and activity decrease throughout pregnancy, while the PS‐specific activity decreases in the second and third trimesters.