A woman of child-bearing age typically experiences her menstrual period every month, with a regularly recurring pattern in most cases. Most women have a period that lasts 3 to 5 days, with a duration of 2 to 7 days considered normal, according to the Office on Women's Health at the U.S. Department of Health and Human Services. For some women, menstrual flow may be preceded by light, intermittent bleeding, called premenstrual spotting. This can be a normal occurrence that doesn't signal a problem, but in rare cases it may indicate a hormonal imbalance or other health problem.
A Normal Occurrence
When an adolescent girl enters puberty and begins having a monthly period, she might experience some irregularity at first, which can include spotting before normal menstrual flow begins. Each month, through a complex series of changes in hormonal patterns, the ovary releases an egg at ovulation, followed by buildup of the uterine lining that is promoted by progesterone. Eventually, decreasing progesterone levels cause the uterine lining to slough off, producing the menstrual flow. During the first few cycles, the pattern of these hormonal changes may be a bit irregular, with progesterone levels being unusually low or dropping prematurely; this can cause premenstrual spotting. With time, menstrual cycles usually become more regular and premenstrual spotting ceases after the first few cycles.
When a woman begins a regimen of hormone-containing birth control pills, she might experience some blood spotting preceding her period, especially for the first few months. Hormones contained in birth control pills, typically estrogen and progesterone, interact with a woman's pituitary gland to suppress other important hormones involved with the menstrual cycle. Sometimes it can take a few months for these interactions to stabilize, and premenstrual spotting might occur during those cycles. This situation usually resolves and periods become regular as a woman's body adjusts to the birth control medications. If a woman who isn't taking birth control pills experiences premenstrual spotting, this could indicate that she's producing too much estrogen during the first half of the cycle, leading to overgrowth of the uterine lining, or too little progesterone during the second half. Either of these hormonal abnormalities can cause early, light bleeding that precedes menstrual flow. Although usually not a serious problem, these types of hormonal irregularities might make it difficult for a woman to conceive if they're not corrected.
Less commonly, a problem not related to the menstrual cycle could be responsible for premenstrual spotting. For example, a cancer of the uterus, such as endometrial cancer, might cause abnormal spotting, and a vaginal or uterine infection might also cause a discharge tinged with blood. Although spotting caused by these conditions could occur at any time during the month, a woman might only notice the problem when she checks for an expected period. If a woman has a bleeding disorder that makes her blood slow to clot, such as Von Willebrand disease, she could be prone to excess bleeding in general and might experience premenstrual spotting.
Seeing a Doctor
Although most cases of premenstrual spotting are not serious, if you experience this problem regularly or it worsens, if your menstrual flow is exceptionally heavy once it begins or if you experience excessive and unusual pain during your period, you should consult your doctor. She will discuss possible causes with you and, if warranted, recommend special tests to identify the underlying cause of your premenstrual spotting.