What happen to the uterus lining during days1-12days as estrogen is rising?

During days 1-12 of the menstrual cycle, as estrogen levels rise, the uterine lining (endometrium) begins to thicken and grow in preparation for a potential pregnancy. Estrogen stimulates the proliferation of the endometrial cells and promotes the development of blood vessels within the lining. This phase, known as the follicular phase, is crucial for creating a supportive environment for a fertilized egg. If fertilization does not occur, this thickened lining will eventually shed during menstruation.