Some girls will have a temporary delay in starting their periods. Absent periods can also be the result of an underlying health problem.
The medical term for not having a period despite being the expected age is primary amenorrhoea.
There can be different causes of primary amenorrhoea depending on whether you also have other signs of sexual development, such as breast growth, pubic hair and development of your genitals.
These are the main reasons for your periods being absent if you do have other signs of sexual development:
- delayed periods - some girls just tend to take longer than average to have their first period; this is often the case if their mother or older sister(s) also took longer
- birth defects - although very uncommon, it’s possible for baby girls to have problems in the development of their reproductive system, such as having no womb, ovaries or vagina
- androgen insensitivity syndrome - a rare genetic condition (affecting around 1 in every 20,400 births) in which a baby can be born with external female genitals but internal male genitals
If you do not have any other signs of sexual development, then possible causes for your absent periods are:
- severe weight loss, often related to an eating disorder such as anorexia nervosa
- stress
- Turner syndrome – a genetic condition, affecting around 1 in every 2,000 girls, which causes those affected to be born with ovaries that do not produce the hormones required to trigger the menstrual cycle
- Kallmann syndrome – another rare genetic condition (affecting around 1 in every 10,000 births) where hormones normally used to trigger sexual development are missing
Common causes for periods suddenly stopping (secondary amenorrheoa) are detailed below.
Unexpected pregnancy
Becoming pregnant without realising it is a surprisingly common cause of an absent period.
This can often occur when your method of contraception fails without you realising it.
Polycystic ovary syndrome
Polycystic ovary syndrome (PCOS) is a common condition responsible for as many as one in three cases of missing periods.
The features of PCOS include:
- a number of cysts (fluid-filled sacs) developing around the edge of the ovaries (polycystic ovaries)
- failure of the ovaries to release eggs (ovulate)
- a higher level of male hormones than normal, or male hormones that are more active than normal
As well as causing absent periods, other symptoms of PCOS include excessive body hair, problems getting pregnant and weight gain.
Hypothalamic amenorrhoea
The menstrual cycle is regulated by part of the brain known as the hypothalamus, which produces hormones that cause the ovaries to release eggs.
In cases of hypothalamic amenorrhoea, the hypothalamus stops producing these hormones and the menstrual cycle stops.
Exactly why the hypothalamus does this is unclear, but evidence has identified three triggers of hypothalamic amenorrhoea:
- excessive weight loss – having a body mass index (BMI) of 19 or less can often trigger hypothalamic amenorrhoea (use the BMI calculator to check your BMI)
- excessive exercise
- stress
Hypothalamic amenorrhoea is particualry widespread in women whose profession requires a combination of physical fitness and maintaining a low body weight, such as athletes and dancers.
Even if you are not concerned about not having a period, you should still seek medical advice if you think you have hypothalamic amenorrhoea, as it can lead to brittle bones (osteoporosis) and put you at risk of a bone fracture.
Hyperprolactinemia
Hyperprolactinemia means you have excessively high levels of a hormone called prolactin in your body.
High levels of prolactin are normally only required after birth, as they help stimulate the production of breast milk. Having high levels at other times can disrupt the normal menstrual cycle and lead to absent periods.
Hyperprolactinemia is thought to affect around 1 in every 200 women and can have a wide range of causes, such as:
Hyperprolactinemia can also arise as a side effect of certain treatments and medications, such as:
- radiotherapy
- antidepressants
- calcium channel blockers, a medication used to treat high blood pressure
- omeprazole, a medication used to treat stomach ulcers
Women who regularly use the drug heroin often develop hyperprolactinemia.
Ovarian failure
Ovarian failure is when the ovaries stop producing eggs in women who should still be young enough (usually 40 or younger) to ovulate.
It is estimated that ovarian failure affects:
- 1 in every 1,000 women aged 30 or younger
- 1 in every 250 women aged 30-35
- 1 in every 100 women aged 40
It is thought that many cases of ovarian failure are caused by the immune system malfunctioning and attacking the ovaries.
Again, you should seek medical advice if you suspect you have ovarian failure, even if you are not concerned about having periods. This is because having this condition can put you at risk of osteoporosis and heart disease.
Thyroid conditions
The thyroid gland is found in the neck. It produces hormones that are released into the bloodstream to control the body's growth and metabolism. They affect processes such as heart rate and body temperature, and help convert food into energy to keep the body going.
In some women the thyroid gland can:
- produce too many hormones – this is known as having an overactive thyroid gland or hyperthyroidism
- not produce enough hormones – this is known as having an underactive thyroid gland or hypothyroidism
Both hyperthyroidism and hypothyroidism can cause absent periods.
