If your period is starting, stopping, and starting again, you’re not alone. About 14 to 25 percent of women have irregular menstrual cycles, according to the National Institutes of Health.

Irregular menstrual cycles may be:

  • shorter or longer than normal
  • heavier or lighter than normal
  • experienced with other problems

The average woman loses about two to three tablespoons of blood during her period. The menstrual blood is partly blood and partly tissue from the endometrial lining on the inside of the uterus. It passes from the uterus through the cervix and out of the body through the vagina.

The endometrial lining doesn’t always separate from the uterus at a steady pace. This is why you might have lighter and heavier days.

If some tissue temporarily blocks the flow out the cervix, it may result in light flow, followed by heavier flow when it passes. This may also create the start, stop, start again pattern.

Generally, day-to-day variations in flow are considered normal if your period lasts around 3 to 7 days.

When you get your period, your levels of estrogen and progesterone are low.

In the first 4 or 5 days, your pituitary gland increases output of follicle-stimulating hormone (FSH) and your ovaries start producing more estrogen.

Between days 5 and 7, estrogen levels typically crest, your pituitary gland releases a surge of luteinizing hormone (LH), and your progesterone levels start to increase.

A shift in hormone levels could create the appearance of a stop-and-start pattern.

Although hormone levels play a major role in your cycle, other factors that can affect your period include:

Period flow or regularity issues could be affected by a variety of health conditions, including:

  • Fibroids, which are abnormal benign growths that develop in or on the uterus.
  • Endometriosis, which occurs when endometrial tissue grows outside the uterus.
  • Polycystic ovary syndrome (PCOS), which occurs when the ovaries make large amounts of androgens (male hormones). Sometimes, small fluid-filled sacs (cysts) form in the ovaries.

See your doctor if:

  • You experience unusually heavy bleeding (needing more than one tampon or pad every hour for a few hours).
  • You have a period that lasts more than 7 days.
  • Your periods stop for more than 3 months and you’re not pregnant.
  • You have vaginal bleeding or spotting between periods or postmenopause.
  • Your periods become very irregular after you have had regular cycles.
  • You experience nausea, vomiting, or severe pain during your period.
  • Your periods are less than 21 days or more than 35 days apart.
  • You experience unusual vaginal discharge.
  • You have the symptoms of toxic shock syndrome, such as fever over 102°F, dizziness, or diarrhea.

Every woman experiences her period differently. Generally, as long as your period lasts around 3 to 7 days, reasonable day-to-day variations in flow are considered normal.

Even though periods might differ from woman to woman, consistency in the way you experience yours is important. If you experience major changes in your period, including having a few that start, stop, and start again, discuss these changes with your doctor.

If you experience serious changes such as the symptoms of toxic shock syndrome, unusually heavy bleeding, or a period that lasts for more than 7 days, see your doctor right away.