Why is a missed period usually the first sign of a pregnancy (explain using hormones?
During a normal menstrual cycle, the hormone levels in a woman's body fluctuate to prepare the uterus for a potential pregnancy. The two main hormones involved in this process are estrogen and progesterone.
Estrogen levels rise during the first half of the menstrual cycle, leading to the maturation of the egg and the thickening of the uterine lining. Around ovulation, there is a surge in luteinizing hormone (LH) that triggers the release of the egg from the ovary.
If fertilization does not occur, the levels of estrogen and progesterone drop, signaling the body to shed the uterine lining in the form of a menstrual period. However, if fertilization does occur, the fertilized egg implants into the uterine lining and signals the body to maintain high levels of progesterone to support the pregnancy.
Therefore, a missed period is usually the first sign of pregnancy because the body maintains high levels of progesterone to support the pregnancy, preventing the shedding of the uterine lining and the onset of menstruation.