Abstract:
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.
