Morphology of haemostasis in menstrual endometrium

Light microscopy, electron microscopy and immunofluorescence were used to study the endometrium from nine uteri removed during the first 72 hours of normal menstruation. During premenstrual spotting, stromal disintegration and vessel lesions without any haemostatic reaction were seen. Up to 20 hours after the onset of menstrual bleeding, blood extravasation was prominent in the functional endometrium. The vessels in this layer were partly or totally sealed by intravascular thrombi functioning as haemostatic plugs. The thrombi contained various amounts of platelets and fibrin and were shed with the tissue. New plugs formed up-stream in the same vessels. Twenty hours after the onset of menstruation, most of the functional endometrium had been desquamated. From 20 to 72 hours after the start of menstrual bleeding no or few thrombi were seen. Haemostasis may then be caused by adherence of vessel lips.