Progesterone does not thicken the endometrium of the patient, rather it counteracts the thickening of the endometrium of the patient and thins the thickened endometrium, also known as thinning of the endometrium. The hormone that thickens the endometrium is estrogen. After menstruation, the follicles secrete estrogen, which increases the level of estrogen in women, and the endometrium of the patient increases in value and thickness under the effect of estrogen level. After ovulation, the corpus luteum mainly secretes progesterone, and the progesterone level will gradually rise and reach its peak. When progesterone acts on the endometrium, the proliferated endometrium will be transformed into the secretory endometrium, and the endometrium will not be significantly thickened again.