Why does menstruation stop during pregnancy?

Menstruation stops during pregnancy because the body undergoes specific hormonal changes to support the developing fetus. When a fertilized egg implants in the uterus, cells from the blastocyst release hormones that prolong the life and activity of the corpus luteum.1

This continued activity ensures the ongoing production of progesterone, which maintains the endometrium (uterine lining) rather than allowing it to break down and be shed as it would during a standard menstrual cycle. Additionally, these hormonal shifts inhibit further ovulation, preventing the release of more eggs while the pregnancy is maintained. As the pregnancy progresses, the placenta takes over the production of necessary hormones, further supporting the uterine environment and ensuring the absence of menstruation, a condition known as amenorrhea.1234