A comparison of mechanisms underlying disturbances of bleeding caused by spontaneous dysfunctional uterine bleeding or hormonal contraception.

Recent research has not been able to demonstrate close endometrial morphological correlations with specific abnormalities of menstrual bleeding, but has pointed to an increasing number of molecular mechanisms that may be involved in the occurrence of certain forms of abnormal uterine bleeding. Ovulatory and anovulatory dysfunctional uterine bleeding (DUB) and progestogen-related breakthrough bleeding (BTB) are three conditions with quite different clinical characteristics. It is also probable that the local endometrial molecular mechanisms associated with these three menstrual disturbances are quite different. Ovulatory DUB is associated with a series of vascular and haemostatic disturbances that all appear to contribute to increased loss of blood and tissue fluid at menstruation. Anovulatory DUB is associated with obvious disturbances of endometrial histology, vascular morphology and fragility, with variable and increased blood flow. Progestogen-related BTB is associated with a multitude of morphological and functional endometrial changes that appear to relate predominantly to a patchy capillary origin for the bleeding. Many molecular and cellular changes have been observed in all three conditions. It is not yet known whether there is a single, but different, underlying mechanism responsible for these multiple abnormalities in each of the three clinical situations.