Aim: To the best of our knowledge, no previous studies have addressed the association of unexplained infertility with protein S activity. This case-control study was performed to evaluate the prevalence of protein S activity in women with unexplained infertility and to compare its prevalence in normal fertile women.
Materials and Methods: This is a case-control study conducted to evaluate the prevalence of protein S activity in
women with unexplained infertility conducted at Ain-Shams University Maternity Hospital. A total of 30 women with
unexplained primary infertility and another 30 fertile women of matched age group as their control were recruited from
September 2018 to March 2019. Using STA Compact Max® Coagulation System protein S was measured. STA-staclot kit
supplied by Stago, France is a clotting assay for measuring protein S activity in human citrated plasma. A venous blood
sample (3 ml) was collected from every participant at any day of the menstrual cycle then the samples were collected
in (3.2%) sodium citrate tubes (venous blood must be mixed with the sodium citrate immediately after collection by
turning upside down gently the tube 3 or 4 times), then centrifugation performed as fast as possible less than an hour to
obtain platelet-poor plasma and centrifuged at 2500g for 15 min (platelet poor plasma). Samples and test reagents are
loaded into the instrument where sample handling, reagent delivery, analysis, and reporting of results are performed
automatically.  Results: This study failed to find a relationship between protein S activity and unexplained infertility compared to the normal fertile population. Despite finding none in the unexplained infertility sample population with protein S deficiency and one in the control group, this difference failed to reach significance.
Conclusion: In conclusion, this study failed to find any association between protein S activity and unexplained infertility
but this study showed that the mean of protein S percentage in group 1 (cases) is lower than the mean in group 2 (controls).