Reasons for Getting Your Period Early

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 1. 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 menstruation is 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 1. 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 early periods. High levels of intense exercise, significant weight loss or gain, a medical illness and mental stress may lead to an occasional early period.

Birth Control

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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.

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.

Nonmenstrual Bleeding

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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.