Ask Your Doctor
Missed a Pill?
A story of hormones in flux
Fact: the female sex hormones that control your menstrual cycle naturally rise and fall throughout the month, as shown in the chart below. It's a dynamic process that repeats itself every 28 days, on average.
A few additional facts
- The hormones estrogen and progesterone control the whole process
- Menstrual cycles vary in length: some last longer than 28 days, while others are shorter
- The menstrual cycle can be thought of as having 4 different phases:
- Menstruation, the stage during which a woman gets her period
- The preovulatory (follicular) phase, when her body is preparing for ovulation
- Ovulation, a woman's most fertile period, when her body releases an egg
- The postovulatory (luteal) phase, essentially the lead-up to menstruation, when the whole cycle begins again
- The average woman will have approximately 500 periods in her lifetime
- Some women bleed for only 3 or 4 days4; others bleed for a week
- The average amount of blood lost in a single period is usually in the range of 30-40 mL2,3 with an upper limit of 80 milliliters1
- If you have excessive blood loss that interferes with your physical, emotional, social or material quality of life, ask your doctor about dealing with heavy periods
Sex Hormone Levels Vary During the Menstrual Cycle
Your cycle in close-up
Although the duration of each phase of the menstrual cycle can vary, the basic sequence of events does not.
Day 1: Your period
The first day of your period is considered Day 1 of your cycle. At this time, estrogen and progesterone, the 2 main types of reproductive hormones, are at low levels.
Day 5: One egg is selected
Days 6-14: Preparing for ovulation
Toward the end of this stage, estrogen levels rise slowly, then more rapidly.
Around Day 14: Ovulation
The follicle surrounding the egg breaks open and the ovary releases the egg into the fallopian tube so it can be fertilized by sperm. The follicle remains in the ovary.
Days 15-28: After ovulation
After ovulation has occurred, levels of progesterone start to increase. If the egg that was released is not fertilized, estrogen and progesterone levels drop after approximately 2 weeks and the lining of the uterus gets ready to be shed. Your next period begins and the cycle starts again.
- Hallberg L, Hogdahl AM, Nilsson L, Rybo G. Menstrual blood loss—a population study. Variation at different ages and attempts to define normality. Acta Obstet Gynecol Scand. 1966;45:320-351.
- Fraser IS, Weisberg E, Minehan E, Johansson ED. A detailed analysis of menstrual blood loss in women using Norplant and Nestorone progestogen-only contraceptive implants or vaginal rings. Contraception. 2000;61:241-251.
- Hale GE, Manconi F, Luscombe G, Fraser IS. Quantitative measurements of menstrual blood loss in ovulatory and anovulatory cycles in middle- and late-reproductive age and the menopausal transition. Obstet Gynecol. 2010;115(2 pt 1):249-256.
- National Institute for Health and Clinical Excellence. 2007. Heavy Menstrual Bleeding. Clinical Guideline. London, UK: National Institute for Health and Clinical Excellence.
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Last updated: January 2014