When periods (menstruations) come regularly, this is called the menstrual cycle. Having regular menstrual cycles is a sign that important parts of your body are working normally. The menstrual cycle provides important body chemicals, called hormones, to keep you healthy. It also prepares your body for pregnancy each month. A cycle is counted from the first day of one period to the first day of the next period. The average menstrual cycle is 28 days long. Regular cycles can range anywhere from 21 to 35 days in adults and from 21 to 45 days in young teens. While uncommon, it is possible to have longer or shorter cycles, but if your period falls out of the normal range, it’s advisable to see a doctor.
In the first half of the cycle, levels of estrogen (a hormone) start to rise. Estrogen plays an important role in keeping you healthy, especially by helping you to build strong bones and to help keep them strong as you get older. Estrogen also makes the lining of the uterus (womb) grow and thicken. This lining of the womb is what will nourish the embryo if a pregnancy happens. At the same time the lining of the womb is growing, an egg, or ovum, in one of the ovaries starts to mature. At about day 14 of an average 28-day cycle, the egg leaves the ovary as a sign that it is ready to be fertilized. This is called ovulation.
After the egg has left the ovary, it travels through the fallopian tube to the uterus. Hormone levels rise and helps prepare the inner lining of the uterus for pregnancy. A woman is most likely to get pregnant during the 3 days before or on the day of ovulation. Keep in mind, women with cycles that are shorter or longer than average may ovulate before or after day 14.
A woman becomes pregnant if the egg is fertilized by a man’s sperm cell and attaches to the wall of the uterus. If the egg is not fertilized, it will break apart. Then, hormone levels drop, and the thickened lining of the uterus is shed which is what makes up your menstrual period.