Women's Health

Irregular Periods: Why Is My Period Late?

Maybe you’re in your mid-to-late 20s and and suddenly — after having regular periods for more than a decade — your cycle suddenly stops behaving like clockwork. You’re not pregnant, and you’re nowhere near menopause, so what’s the deal?

Irregular periods aren’t always a sign of a problem. We break down what you should know about how to identify irregular periods, what causes them and when to see a doctor.

Why is My Period Late?

During a normal menstrual cycle, an egg is released from one of your ovaries during ovulation. If the egg is not fertilized by a sperm, then changing hormone levels send your body a signal to shed the blood and tissues that line your uterus. This bleeding typically lasts about five days. Then, the monthly cycle repeats itself. But some women have what is called abnormal uterine bleeding — another term for irregular periods — which can happen for a variety of reasons, from stress and lifestyle factors, to more serious underlying medical conditions.

What is an Irregular Period?

An irregular period is when the length of your menstrual cycle unexpectedly falls outside of your regular range. Irregular periods can include abnormal uterine bleeding, such as:

  • Bleeding or spotting between periods
  • Bleeding after sexual intercourse
  • Heavy bleeding during your period
  • Menstrual bleeding that lasts longer than normal
  • Bleeding after you’ve reached menopause

After puberty, many women have a regular menstrual cycle. However, it’s normal for the cycle to vary by a few days each time. According to the American Academy of Family Physicians (AAFP), between nine and 14 percent of women have irregular periods between their first period and menopause.

Reasons for a Late Period, Missed Period or Irregular Period

There are a number of reasons why you may have an irregular, missed or late period, ranging from stress to more serious medical conditions.

Common causes of irregular periods include:

  • Uncontrolled diabetes — If you have uncontrolled diabetes, you may have irregular periods because the interaction between your blood sugar levels and hormones can disrupt your menstrual cycle.
  • Eating disorders — If you have an eating disorder, such as anorexia or bulimia, you may have irregular or missed periods. This is because your body is not producing and circulating enough hormones to control your menstrual cycle.
  • Hyperprolactinemia — Women who have too much of a protein hormone called prolactin in their blood can have irregular periods.
  • Medications — Certain medications, including anti-epileptics and antipsychotics, can cause irregular periods.
  • Polycystic ovary syndrome — PCOS is caused by imbalanced sex hormones, which can disrupt regular menstruation.
  • Premature ovarian failure — The ovaries of women with POF stop working before the age of 40, according to the National Institutes of Health. However, some women with this condition continue to have occasional periods.
  • Stress — Stress hormones can affect menstruation and prolonged stress can cause your period to be delayed or for you to skip it entirely.

Also, when you first begin menstruating, it may take some time time before your period becomes regular. Your period may become irregular up to eight years before menopause.

What to Do When Periods are Late

If you experience any of the following symptoms, it may be time to talk to your doctor:

  • You haven’t had a period for 90 days
  • Your period suddenly becomes irregular
  • You have a period more often than every 21 days
  • You have a period less often than every 35 days
  • Your period lasts for more than a week
  • Your period becomes unusually heavy
  • You bleed between periods
  • Your periods are extremely painful

A gynecologist will be able to determine the cause of your irregular periods and help you develop the best treatment plan for you.

When to call your healthcare provider

There are several possible causes of irregular periods, many of which require medical treatment. Make an appointment to see your doctor if:

  • your periods stop for more than 3 months and you’re not pregnant
  • your periods become irregular suddenly
  • you have a period that lasts longer than 7 days
  • you need more than one pad or tampon every hour or two
  • you develop severe pain during your period
  • your periods are less than 21 days or more than 35 days apart
  • you experience spotting between periods
  • you experience other symptoms, such as unusual discharge 

Your doctor will ask about your medical history and want to know about:

  • any stress or emotional issues you’re experiencing
  • any changes to your weight
  • your sexual history
  • how much you exercise

Medical tests may also be used to help diagnose the cause of your irregular bleeding, including:

  • a pelvic examination
  • blood tests
  • pelvic and transvaginal ultrasound