Introduction: Protein S (PS) activity has been shown to decrease during normal pregnancy. The aim of this study was to determine any correlation between decreased maternal PS activity and fetal growth restriction (FGR). Methods: We carried out a retrospective study of maternal PS activity and complement 4b-binding protein (C4BP) concentration in 102 patients with FGR and 58 patients with fetuses that had normal growth. Among pregnancies affected by FGR, 14 diagnoses were made in the second trimester and 88 in the third trimester. Patients whose fetuses had normal growth were matched with FGR subjects for maternal age and gestational age at sampling (29 cases each in the second and third trimester). Results: Mean PS activity of the control group in the third trimester was significantly lower than in the second trimester (56.5 ± 16.5% vs 35.8 ± 13.8%). PS activity in women with FGR was significantly decreased in both the second trimester (36.6 ± 13.2%) and third trimester (30.2 ± 12.2%) compared with control group levels. Plasma concentrations of C4BP for the control group were significantly higher in the third trimester than in the second trimester (90.5 ± 17.5% vs 81.1 ± 13.6%). However, in women with FGR, plasma C4BP concentrations in both the second trimester (84.0 ± 14.8%) and the third trimester (86.0 ± 17.7%) were comparable with concentrations of the control group. Conclusions: Maternal PS activity decreased as normal pregnancies progressed but decreased over time in cases with FGR. Excessive decreases in PS activity during pregnancy could contribute to development of FGR.
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