When periods (menstruation) comes regularly, this is called menstrual cycle. Having regular menstrual cycles means that essential parts of your body are working fine. The menstrual cycle supplies important body chemicals (known as hormones) to keep you healthy, and prepares your body for pregnancy each month. The first day of one period flow marks the beginning of a cycle, and ends on the first day of the next period flow. On average, a menstrual cycle is 28 days long, but regular cycles can range from 21 to 35 days long for adults, and from 21 to 45 days for young teens. It’s also possible to have cycles that are longer or shorter, but such cases are not so common. If your menstrual cycle is not within the normal range, it’s best to see a doctor.
During the first half of the menstrual cycle, estrogen (a hormone) levels begin to rise. Estrogen is important for your health because it helps build strong bones, and keeps them fit as you get older. Estrogen also makes the lining of the uterus (womb) grow and thicken, which nourishes the embryo if a pregnancy occurs. As the lining of the uterus grows, an egg cell (or ovum) in one of the ovaries begin to mature. In an average 28-day cycle, ovulation occurs on the 14th day wherein the egg cell leaves the ovary as a sign that it is ready for fertilization.
After leaving the ovary, the egg cell then travels through the fallopian tubes to get to the uterus. At this point, hormone levels rise and help prepare the lining of the uterus for pregnancy. Chances of getting pregnant are higher during the three days before, or on the day of ovulation. Note that women who have cycles shorter or longer than average may ovulate before or after the 14th day.
Pregnancy happens when a woman’s egg cell is fertilized by a man’s sperm cell, and attaches to the wall of the uterus. If there was no fertilization, the egg cell will dissolve, hormone levels will drop, and the thickened lining of the uterus will shed, which makes up the menstrual period.