How does the endometrium get thicker and thicker?

The endometrium thickens in response to hormonal changes during the menstrual cycle, primarily due to estrogen produced by the ovaries. Following menstruation, estrogen stimulates the proliferation of endometrial cells and the growth of blood vessels, leading to a thicker uterine lining. This process prepares the endometrium for potential implantation of a fertilized egg. If pregnancy does not occur, hormone levels drop, leading to the shedding of the endometrial lining during menstruation.