What we now know is that the S protein damages endothelial cells. These line vascular system vessels. Additionally the protein may cause clumping, and we are seeing cases of clots. So we get at minimum both clumps to block vessels and cell damage that probably causes rough surfaces. The combination effect probably is independent of sex hormones. However, men and women have some differences in iron content in blood. I expect that menstruation exposes women to clotting risk more than men simply because the more you bleed, the more clotting will occur anyway. But for any pilot bleeding at altitude, and then if it forms a traveling clot and then a blockage somewhere, well, there you have a chance of heart attack or a stroke. Ahhh - perhaps all pilots should take aspirin as a preventative? Since it is a blood thinner. Though not a clot preventer.