Missing a period often leads sexually active women to consider pregnancy as a possible cause but there are several other causes for a delayed or missed period. The average menstrual cycle is 28 days but it varies widely from 21 to 35 days. Some women get their periods with clockwork regularity while others may get a period  either a few days early or a few days late which can still be considered normal. There are many conditions, however, that can cause an abnormally lengthy delay in menstruation which is known as amenorrhea.  Secondary amenorrhea is a delay in the periods beyond 3 months in a woman who previously had regular periods. Normally, a girl starts her first periods at the age of 11 or 12 years but in some cases it may be delayed till the age of 15 or 16. Primary amenorrhea is when a girl has not had her first periods even by the age of 16. Read more on causes of primary and secondary amenorrhea.

Causes of Delayed Periods

  • Pregnancy causes a cessation of periods due to the hormonal changes associated with fertilization and the growing fetus.
  • Stress
  • Severe acute or chronic illness
  • Lactation. Periods after childbirth may be delayed in mothers who breastfeed. However, a woman may become pregnant even while lactating, so a late period could also be a sign of pregnancy.
  • Drugs such as contraceptives can delay periods. Women sometimes take hormones in the form of combined pills or progesterone when they want to postpone their periods.
  • Obesity
  • Drastic weight loss
  • Eating disorders such as anorexia or bulimia
  • Excessive exercise
  • Menstrual cycle disorders
  • Thyroid disease
  • Hormonal imbalance, as in polycystic ovarian syndrome (PCOS).
  • Perimenopause which is the the time before menopause begins.
  • Primary amenorrhea. If breast development and other sexual characteristics are present in a girl by the age of 14 but her periods are delayed, it may not be a cause for concern. However, if she has still not had her periods by the time she is 16 years of age, investigations will be necessary to find the cause of her delayed periods which is then known as primary amenorrhea.
  • Periods may be delayed or be irregular in the first few months after the start of menstruation (menarche).
  • Pituitary tumors

Diagnosis of the Cause of Delayed Periods

It is important to arrive at a diagnosis so that the correct treatment can be prescribed for the cause of delayed periods. A thorough history, particularly the menstrual history, and physical examination, including a pelvic examination should be conducted.

  • Pregnancy test. This should be done to rule out or confirm pregnancy. A repeat pregnancy test may be done after one week if the first test is negative.
  • Progestin withdrawal test to see if there is withdrawal bleeding following administration of hormones for 7 to 10 days.
  • Blood tests :
    • Hormones
      • estradiol
      • testosterone
      • prolactin
      • follicle stimulating hormone (FSH)
      • luteinizing hormone (LH)
    • Thyroid function tests
  • Ultrasound
  • Hysterosalpingogram (HSG)
  • MRI / CT scan

Article reviewed by Dr. Greg. Last updated on April 17, 2011