Faught W, Garner P, Jones G, Ivey B
Department of Obstetrics and Gynecology, University of Ottawa, Ontario, Canada.
Am J Obstet Gynecol. 1995 Jan;172(1 Pt 1):147-50. doi: 10.1016/0002-9378(95)90104-3.
The objective of the study was to determine the normal changes in the plasma concentrations of protein C and protein S that occur during each trimester of pregnancy.
The study was a prospective cross-sectional study of 91 normal pregnant women who had plasma concentrations of protein C and protein S measured during the first, second, and third trimesters.
There was no statistically significant change in antigenic or functional protein C levels during normal pregnancy. Total protein S levels also remained unchanged. Free protein S levels fell significantly from first to second trimesters (0.45 U/ml mean to 0.26 U/ml mean, p < 0.001), but no further fall occurred during the third trimester.
The second-trimester fall in free protein S levels is a physiologic pregnancy adaptation. Women with a thromboembolic event appearing for the first time during pregnancy should have investigations for protein S deficiency delayed until the postpartum period, to avoid misdiagnosis and treatment.
