Missed Periods (Amenorrhea) Causes of Delayed Periods

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.

What is amenorrhea?

Amenorrhea is the medical term for absent menses (no period). Missing a single period is not considered as amenorrhea although this should not occur in a healthy female unless there are short term disturbances. Amenorrhea is a total lack of menstruation that occurs for 6 months or more. There are two types of amenorrhea – primary and secondary amenorrhea.

Primary amenorrhea is when a girl has not had her first periods even by the age of 16. 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.

Period Pain

Types of Amenorrhea

Primary amenorrhea is the lack of menstruation in a girl who is 16 years or older or if there are signs of puberty present for more than 2 years with no menses. This means that menarche (the onset of menstruation) has not occurred as yet under the the abovementioned conditions.

Secondary amenorrhea is when menses is absent for 6 consecutive months or more in a girl or woman who was previously menstruating. Pregnancy and menopause are two common causes that are not pathological but there are other causes that may be a result of minor or serious medical conditions.

Causes of Delayed Periods

Since menstruation is controlled by a cyclic play of hormones involving multiple structures in the body, any dysfunction or abnormality in any of these organs may be the cause of amenorrhea. The organs involved in ovulation and menstruation are the hypothalamus, pituitary gland, ovaries, uterus and the vagina.


The hypothalamus secretes gonadotropin-releasing hormone (GnRH), which then acts on the pituitary gland, triggering the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH).

Some of the causes for a deficiency or lack of gonadotropin-releasing hormone (GnRH) include :

  • Genetic disorders.
  • Starvation or malnutrition.
  • Eating disorders like anorexia or bulimia.
  • Excessive dieting and exercise.
  • Trauma to the brain.
  • Tumors of the hypothalamus.
  • Irradiation of the hypothalamus, either accidental or induced due to radiation therapy.
  • Narcotic use and alcohol abuse.
  • Certain drugs, especially psychoactive drugs.
  • Infections like tuberculosis and HIV/AIDS.
  • Other chronic diseases – many chronic disorders of vital organs in the body may affect the hypothalamus.
  • Psychological or psychiatric conditions like depression and schizophrenia.
  • Mental and/or emotional stress.

Pituitary Gland

The pituitary gland is stimulated by gonadotropin-releasing hormone (GnRH) from the hypothalamus. Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the pituitary gland then act on the ovaries, triggering ovulation and estrogen production.

Some of causes of amenorrhea due to pituitary dysfunction include :

  • High levels of prolactin (hyperprolocatinemia).
  • Trauma to the brain.
  • Tumors of the pituitary gland and surrounding brain tissue.
  • Infections like TB.
  • Degeneration of the pituitary gland.

Breastfeeding stimulates the production and secretion of prolactin. This may contribute to amenorrhea in breastfeeding mothers.


The ovaries are stimulated by follicle-stimulating hormone (FSH) and luteinizing hormone (LH) to mature and release an egg cell (ovum). It also secretes estrogen and progesterone to facilitate implantation of the embryo in the event of conception.

In most cases of amenorrhea, ovulation does not occur (anovulation). This is known as anovulatory amenorrhea. However at times, ovulation may occur although menstruation is absent and this is referred to as ovulatory amenorrhea.

Some ovarian causes of amenorrhea include :

  • Genetic disorders.
  • Polycystic ovary syndrome (PCOS).
  • Autoimmune diseases like Hashimoto’s thyroiditis.
  • Infections like mumps and complications of untreated bacterial vaginosis.
  • Irradiation of the pelvis, either accidental or due to radiation therapy.
  • Drugs like chemotherapy and hormone contraceptives.
  • Chronic conditions like diabetes.

Uterus & Vagina

If pregnancy does not occur after ovulation , the endometrial lining of the uterus will slough off and menstruation will commence. The menses is then passed out through the vagina. In uterine causes of amenorrhea, ovulation is usually not affected and amenorrhea in this instance is often considered as ovulatory amenorrhea.

Some uterine and vaginal causes of amenorrhea include :

  • Uterine fibroids and polyps causing an obstruction.
  • Infections of the uterus like TB.
  • Incomplete growth and development of vagina and/or uterus (aplasia).
  • Vaginal septum.
  • Hymen that does not perforate.
  • True or pseudo-hermaphroditism (hermaphrodite).
  • Use of an intra-uterine device (IUD).
  • Fertility, abortion and miscarriage surgical procedures like a dilation and curettage (d&c)

Many of the uterine and vaginal causes of amenorrhea are congenital, meaning that it is present from birth (birth defect).

Systemic and Other Causes

Apart from the chronic and systemic causes mentioned above, other conditions that may contribute to amenorrhea include :

  • Thyroid disorders – hyper- or hypothyroidism.
  • Obesity or if severely underweight.
  • High levels of androgens (male sex hormones) due to tumors.
  • Tumors producing high level of estrogen or HCG (human chorionic gonadotropin).
  • Cushing’s syndrome.
  • Sarcoidosis.

It is important to bear in mind that the most common cause of secondary amenorrhea is pregnancy. Menopause or early menopause (premature ovarian failure) is another common cause. These conditions must be excluded before considering further diagnostic investigation to identify the cause of primary or secondary amenorrhea.


Diagnosis for Missed 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


  1. Amenorrhea. Medscape

Last updated on September 2, 2018.

Please note that any information or feedback on this website is not intended to replace a consultation with a health care professional and will not constitute a medical diagnosis. By using this website and the comment service you agree to abide by the comment terms and conditions as outlined on this page