月经结束后的子宫内膜最薄，之后慢慢变厚，可以理解为子宫是房子，每个月建房子（内膜变厚）准备迎接客人，客人没有来，全部拆掉（月经排出）下个月再建新房子，周而复始。
After menstruation, the endometrium is the thinnest, and then it gradually thickens; you may think that the uterus is a house; you build a house every month (the endometrium thickens) to prepare for guests, and if the guests do not come, all of them are demolished (menstruation flows out) and a new house is built next month, which starts again and again.