The formation and regression process of the luteal phase

After ovulation, the follicle forms a corpus hemorrhagicum as the egg is released, which then transforms into the corpus luteum. This leads to an increase in progesterone levels in the body, which acts on the hypothalamic temperature regulation center, causing a rise in basal body temperature and stimulating stromal proliferation of the endometrium. This phase, maintained until menstruation begins, is known as the luteal phase. During this time, the endometrium becomes rich in glycoproteins, creating a favorable environment for implantation of the fertilized egg. If pregnancy does not occur, estrogen and progesterone levels drop sharply about two days before menstruation, causing the endometrium to lose hormonal support and shed—resulting in menstrual bleeding. If pregnancy occurs, the corpus luteum continues to develop into a corpus luteum cyst of pregnancy, secreting progesterone to support the early stages of pregnancy.