A thick endometrium can cause the absence of menstruation, and understanding the reasoning behind this will help you understand why menstruation does not occur after a thickened endometrium. Because the onset of menstruation is mainly due to the withdrawal of the functional layer of the endometrium from with the level of hormones and the resulting interruption of nutrition in the functional layer, which then causes the rupture of cells or tiny blood vessels, causing the onset of menstruation, so if hormones have been present, the nutrition of the functional layer of the endometrium has not been interrupted and there is no rupture, so if the endometrium is thickened in this state and hormones have been continuously supplied, the onset of menstruation will not occur. Since the rupture of the functional layer itself will not occur, the onset of menstruation will not occur. Therefore, if the endometrium has been continuously thick, it means that the hormone level is relatively high and menstruation cannot come.