Irregular Periods

Overview

A menstrual cycle longer than 6 weeks is also abnormal and is called Oligomenorrhoea. Oligomenorrhoea is defined as a cycle length between 6 weeks and 6 months. If periods do not occur at all, it is called amenorrhoea. Amenorrhoea is classified as either primary or secondary. Primary amenorrhoea is when a woman does not have a period by the age of 16. It is also diagnosed if she fails to develop secondary sex characteristics such as pubic hair or breast by the age of 14.

Secondary amenorrhoea is when periods stop for more than 6 months in women of normal reproductive age, who previously had periods. Absent periods can be normal in some circumstances, such as when pregnant or breastfeeding.

Why Does it Occur?

The most common cause of oligomenorrhoea is polycystic ovarian syndrome (PCOS). Oligomenorrhoea is also common in women at the extremes of their reproductive life. Periods are often irregular in teenagers for the first few years after they begin (menarche). They are also usually irregular in older women approaching their last period (menopause).

Oligomenorrhoea is usually related to a failure of the ovary to ovulate consistently. As the cycle is longer than usual, the lining of the uterus is also exposed to more of the hormone oestrogen than usual and becomes thicker. Once the period does eventually start, the bleeding is usually heavier. The treatments of oligomenorrhoea are described in more detail in the sections on polycystic ovarian syndrome and on heavy periods.

The causes of amenorrhoea can be grouped in the following way:

• Abnormalities of the uterus or vagina
• Disorders of the ovaries
• Disorders of the hypothalamus or pituitary gland in the brain
• Other hormonal problems

Abnormalities of the Uterus and Vagina

Some women are born with abnormalities of the uterus and vagina. Women can be born without a uterus and vagina. This is called Rokitansky syndrome. It affects 1 in 4000 women. The ovaries usually function normally. It is usually also associated with abnormal development of the kidneys and renal tract. Another less common problem is a sheet of tissue, or septum (transverse vaginal septum), in the lower third of the vagina, which prevents the outflow of blood. A similar problem is seen in women who are born without an orifice in the hymen (Imperforate hymen). The hymen is the tissue at the opening of the vagina.

Another rare condition is caused by an abnormality of the androgen receptors known as Androgen insensitivity. In these women, the genetics dictate that they should be male (XY chromosomes), but they are not sensitive to the male hormone testosterone produced by their gonads. This results in the development of female external genitalia despite their male genetic make up. The vagina is very short and they do not have a uterus.

The outflow of blood from the uterus can also be blocked at the cervix after surgery, radiation treatment or infection in the neck of the womb (cervical stenosis). Scar tissue within the cavity of the womb can also be caused by surgery (Asherman’s syndrome).

Disorders of the Ovaries

Failure of ovulation can result in infrequent or absent periods. Polycystic Ovarian Syndrome is the most common cause. It can also be caused by a variety of other hormone problem including high levels of prolactin (hyperprolactinaemia).

Some women are born without ovaries or with small non-functioning ovaries (ovarian dysgenesis). This causes primary amenorrhoea and also a failure to develop normal secondary sex characteristics such as breasts and pubic hair. Turner’s syndrome is the most common cause. In this syndrome, women have only one, rather than two X chromosomes. There is a range of severity with Turner’s syndrome. Some women have a mixture of normal and abnormal cell. This is called a mosaic. Tuner’s mosaics can have milder symptoms and rarely can ovulate and be fertile.

Premature menopause can present with primary or secondary amenorrhoea.

Disorders of the Hypothalamus or Pituitary Gland in the Brain

The normal function of the ovary is controlled by hormones produced by the hypothalamus and by the pituitary gland in the brain. The hypothalamus produces gonadotrophin-releasing hormone (GnRH), which stimulates the release of the gonadotrophins, luteinising hormone (LH) and follicle stimulating hormone (FSH), which in turn act on the ovary.

A variety of conditions can lead to a reduction in gonadotrophin production mediated by the hypothalamus. These include:

• Stress
• Weight loss
• Drugs
• Kallmann’s syndrome is a condition you may be born with. The hypothalamus fails to produce GnRH. Interestingly it also affects the sensation of smell.
• Brain tumours can destroy the hypothalamus.

Abnormal functioning of the pituitary gland can result from:

• Tumours. A prolactinoma is a tumour producing the hormone prolactin. This account for 20% of amenorrhoea
• Sheehan’s syndrome. This causes the pituitary gland to fail to secrete gonadotrophins. It is most commonly caused by massive haemorrhage after the delivery of a baby.

Other Hormonal Problems

A number of other hormonal conditions can cause absent or infrequent periods. These include abnormal function of the thyroid gland and of the adrenal glands.