Estrogen causes ultrastructural changes of fibrin networks during the menstrual cycle: a qualitative investigation.

INTRODUCTION Hormonal fluctuations may influence fibrin structure. During the menstrual cycle, plasma fibrinogen levels change, mainly due to the variations of estrogen. Throughout the menstrual cycle estrogen levels peak twice, first during the mid-follicular phase and then a lower second peak during the luteal phase. MATERIALS AND METHODS In order to investigate the possible changes in the fibrin network throughout the menstrual cycle, the fibrin network ultrastructure of six healthy female participants were studied at different intervals in the menstrual cycle where differences in estrogen levels are prevalent. Blood plasma smears were prepared for scanning and transmission electron microscopy analysis. RESULTS The external and internal structure of the fibrin fibers showed different morphologies throughout the menstrual cycle. The fibrin fibers were smooth during days 1-5. However, during days 12-14 of the menstrual cycle the fibrin fiber morphology started to change, becoming less smooth. During the luteal phase of the cycle (days 20-25), the network appears sticky, where the minor, thin fibers are more prominent between the thick fibers when compared to the menstrual phase. CONCLUSION The two estrogen peaks of the menstrual cycle coincide with the changes seen in the current qualitative research, where the fibrin morphology changes during the same time as the estrogen peaks occur. Purified fibrinogen confirmed that it is indeed estrogen that causes the altered fibrin network morphology. This research is the first to show ultrastructural changes in fibrin fiber morphology resulting from estrogen changes during the menstrual cycle.