Why does the uterus develop a thick and spongy lining every month?

The uterus develops a thick and spongy lining every month as part of the menstrual cycle to prepare for potential pregnancy. This process, known as the proliferative phase, is driven by hormonal changes. After menstruation, rising estrogen levels stimulate the uterine lining (endometrium) to thicken and become enriched with blood vessels, creating a nourishing environment for a fertilized egg. This thickened lining provides an ideal implantation site. If fertilization doesn’t occur, hormonal shifts trigger the breakdown of the lining, leading to menstruation. The cycle then repeats, ensuring the uterus is consistently prepared for the possibility of pregnancy.