What happens during the typical 28-day menstrual cycle?
Day one starts with the first day of your period. The blood and tissue lining the uterus (womb) break down and leave the body. This is your period. For many woman, bleeding lasts from four to eight days. Hormone levels are low. Low levels of the hormone estrogen can make you feel depressed and irritable.
Days one through five
During Days one through five of your cycle, fluid-filled pockets of follicles develop on the ovaries. Each follicle contains an egg.
Days five through eight
Between Days five and seven, just one follicle continues growing while the others stop growing and are absorbed back into the ovary. Levels of the hormone estrogen from the ovaries continue rising. By day eight, the follicle puts out increasing levels of estrogen and grows larger. Usually by day eight, period bleeding has stopped. Higher estrogen levels from the follicle make the lining of the uterus grow and thicken. The uterine lining is rich in blood and nutrients and will help nourish the embryo if a pregnancy happens. Estrogen helps boost endorphins, which are the "feel good" brain chemicals that are also released during physical activity. You may have more energy and feel relaxed or calm.
Day 14
A few days before Day 14, your estrogen levels peak and cause a sharp rise in the level of luteinizing hormone (LH). LH causes the mature follicle to burst and release an egg from the ovary, called ovulation, on Day 14. A woman is most likely to get pregnant if she has sex on the day of ovulation or during the three days before ovulation (since the sperm are already in place and ready to fertilize the egg once it is released). A man' sperm can live for three to five days in a woman's reproductive organs, and a woman's egg lives for 12 to 24 hours. In the few days before ovulation, your estrogen levels are at their highest. You may feel best around this time, emotionally and physically.
Day 15 through 24
Over the next week (Days 15 through 24), the fallopian tubes help the newly released egg travel away from the ovary toward the uterus. The ruptured follicle on the ovary makes more of the hormone progesterone, which also helps the uterine lining thicken even more. If a sperm joins with the egg in the fallopian tube (this is called fertilization), the fertilized egg will continue down the fallopian tube and attach to the lining of the uterus (womb). Pregnancy begins once a fertilized egg attaches to the womb.
Day 24 through 28
If the egg is not fertilized, it breaks apart. Around Day 24, your estrogen and progesterone levels drop if you are not pregnant. This rapid change in levels of estrogen and progesterone can cause your moods to change. Some women are more sensitive to these changing hormone levels than others. Some women feel irritable, anxious, or depressed during the premenstrual week, but others do not.
In the final step of the menstrual cycle, the unfertilized egg leaves the body along with the uterine lining, beginning on Day One of your next period and menstrual cycle.