Your menstrual cycle: A key to understanding your fertility

In understanding your fertility signs, it is very important that you become aware of the changes that take place in your body during the menstrual cycle. Menstruation is the shedding of the inner lining of the uterus when a pregnancy does not occur in that particular cycle. Your estrogen and progesterone levels are very low on the first day of menstruation, day one of your cycle. Estrogen levels begin to increase, stimulating the growth, or proliferation, of the lining of the uterus, in preparation for a pregnancy. Estrogen is the dominant hormone in the first two weeks of the menstrual cycle. Around day 14 of your cycle, and immediately prior to ovulation, estrogen levels peak, triggering a release of an egg from one of the ovaries. Once an egg is released, it can be fertilized for approximately 12 to 24 hours. This is the best time to have intercourse to achieve a pregnancy. Following ovulation, estrogen levels drop and progesterone rises and becomes dominant for the next two weeks. Progesterone causes the uterine lining to mature, becoming more compact, so that it is able to support and nurture a fertilized egg. If implantation of a fertilized egg does not occur, progesterone levels drop, causing the onset of menstruation, within 48 hours (around day 28).