Women in the middle of their childbearing years normally experience fairly regular periods. Cycle length for most women ranges from every 25 to 30 days.
Even if your menstrual cycles usually occur predictably, it's not unusual to experience an early period every now and then. This might occur due to physical or mental stress, a hiccup or side effect related to your birth control method, or a gynecologic or other medical condition.
Age and Life Events
Periods occur due to the cyclic action of female hormones on the lining of the uterus. When menstruation begins during the adolescent years, the hormone regulating systems are not yet fully mature and it may take 6 years or longer for periods occur regularly. Early periods are common during this time.
Periods also occur irregularly when during a woman's perimenopausal years, those leading up to menopause. Perimenopause typically begins during a woman's 40s. Irregular cycles with early or late periods are fairly common at this stage of life because the ovaries function increasingly unpredictably leading up to menopause.
Certain life events can also affect female hormone levels and result in periods that occur earlier than expected. High levels of intense exercise, significant weight loss or gain, a medical illness and mental stress may lead to an occasional early period.
Early periods sometimes occur in women taking birth control pills, especially if you forget to take 1 or more pills in a pack. An intrauterine device, or IUD, can also lead to irregular or early periods — particularly during the first year of use.
If you've taken the emergency contraceptive, morning-after pill levonorgestrel (Afterpill, My Way, Next Choice, Next Choice One Dose, Plan B One Step, Take Action), you might experience a change in your next period. An article published in the February 2010 issue of The Lancet found that among women who used levonorgestrel emergency contraception, their next period came an average of 1.2 days earlier than expected.
Gynecologic and Other Medical Causes
Certain gynecologic conditions can cause irregular menstrual cycles or bleeding that might seem like an early period. With polycystic ovary syndrome, or PCOS, small fluid-filled cysts form in the ovaries that lead to an imbalance in sex hormone levels. Women with PCOS experience irregular periods along with other symptoms, such as weight gain and increased body and/or facial hair.
With endometriosis, cells that normally line the inside of the uterus occur in other parts of the pelvis. Women with endometriosis often experience a shortened menstrual cycle as well as prolonged bleeding, and painful periods and intercourse.
Some medical conditions, such as thyroid disease and uncontrolled diabetes, and certain medications, such as blood thinners, can also cause periods to appear earlier than expected.
Bleeding unrelated to your menstrual cycle might be mistaken for an early period. For example, if you have become pregnant since your last period, you might experience bleeding before your expected period as the embryo implants into the uterus. This type of implantation bleeding is usually lighter than a typical period. Rarely, an infection or cancer might cause a bloody vaginal discharge. Although this discharge can appear anytime, it might be misinterpreted as an early period.
An occasional early period usually represents nothing more than a temporary blip in your hormone levels. If you frequently experience early periods or other menstrual symptoms, such as pain or heavy bleeding, contact your healthcare provider. Tracking your periods over several months with an app or diary might show patterns that can help your doctor identify the cause.
Reviewed and revised by: Tina M. St. John, M.D.
- Menopause: Cycle and Hormone Changes During Perimenopause -- The Key Role of Ovarian Function
- American College of Obstetrics and Gynecology: Menstruation in Girls and Adolescents -- Using the Menstrual Cycle as a Vital Sign
- Family Practice Notebook: Anovulatory Bleeding
- Contraception: Side Effects from the Copper IUD -- Do They Decrease Over Time
- Menopause: Progesterone and Ovulation Across Stages of the Transition to Menopause
- Lancet: Ulipristal Acetate Versus Levonorgestrel for Emergency Contraception: A Randomised Non-Inferiority Trial and Meta-Analysis
- Merck Manual Professional Version: Polycystic Ovary Syndrome (PCOS)