Most adult women in their prime childbearing years have periods on a fairly regular basis, usually about every 28 days. But life events, including stressful situations and significant illnesses, can sometimes disrupt this regularity and cause your periods to occur earlier than expected. Your method of birth control and certain gynecologic or medical conditions might also cause an early period. Contact your doctor if you experience early periods frequently, or if your bleeding is excessive or accompanied by significant pain.
Age and Life Events
Periods are regulated by the complex interaction of hormones produced by two glands in the brain, the hypothalamus and pituitary, and the ovaries. This regulatory system is not fully mature when menstruation begins in adolescence, and it may take up to 6 years for periods to become regular. Thus, early periods are common during a young woman's first few years of menstruating. Periods become irregular again when a woman enters perimenopause, a transitional phase leading to menopause. Perimenopause usually begins around age 45 and lasts roughly 4 years, on average. Ovarian function and periods are commonly irregular during perimenopause, possibly leading to early periods.
Significant life events can also cause fluctuations in hormone levels, leading to menstrual irregularity and early or late periods. Intense physical training, a substantial change in body weight, a major medical illness, and even mental stress may cause an early period.
Birth control pills can cause a period to arrive earlier than usual, especially if you forgot to take 1 or more pills. IUDs are another possible cause of early periods, due to irregular menstrual bleeding. If you've taken an emergency contraceptive containing levonorgestrel (Ella, Next Choice, Plan B), you might experience a change in your next period. An article published in the August 2006 issue of "Contraception" found that about 15 percent of women with regular menstrual cycles who took levonorgestrel for emergency contraception experienced spotting and an early or late period in the cycle following taking the medication.
Certain female reproductive conditions can cause irregular periods or bleeding between periods that can seem like an early period. With polycystic ovarian syndrome (PCOS), small fluid-filled sacs called cysts form in the ovaries and abnormal hormone levels are present. You may have PCOS if your periods are irregular and you have certain other symptoms, including weight gain or excessive male hormone effects -- such as facial hair or baldness. With endometriosis, cells that normally line the uterus grow in other parts of the pelvis. Women with endometriosis sometimes experience irregular menstrual bleeding, which might occur earlier than expected. If your periods are routinely intensely painful, you might have endometriosis. Some medical conditions, such as thyroid disease, and certain medications, such as blood thinners, can also cause early periods.
Not an Early Period After All
It's possible to misinterpret other causes of vaginal bleeding as an early period. For example, if you have become pregnant since your last period, you might experience bleeding before your next expected cycle as the embryo implants into your uterus. This type of bleeding -- called implantation bleeding -- is lighter than a normal period. Uncommonly, an infection or cancer might cause a bloody discharge. Although this discharge can appear any time, it may be noticed at a time when it is misinterpreted as an early period.
If your period comes early once in a while, this is likely a normal occurrence and generally not a cause for concern. But if you frequently have early periods or experience other symptoms -- such as pain, heavy bleeding or unusual vaginal discharge -- see your doctor as soon as possible. Tracking your menstrual cycles with a calendar or an app will help determine whether a period is early and may show patterns that could help your doctor identify the cause.
Reviewed by: Tina M. St. John, M.D.