Why are menstrual cycles absent during pregnancy?

(N/A) The menstrual flow results from the breakdown of the endometrial lining of the uterus and its blood vessels,which forms a liquid that is discharged through the vagina. Menstruation only occurs if the released ovum is not fertilized.
During pregnancy,these stages of the menstrual cycle are suspended. The corpus luteum secretes large amounts of progesterone,which is essential for maintaining the endometrium. These hormonal changes prevent the menstrual flow from occurring during pregnancy. While the absence of menstruation is a primary indicator of pregnancy,it can also be caused by other factors such as stress or poor health.