Irregular periods: which hormone tests do you need?

Irregular periods are one of the most common reasons young women see an endocrinologist. Often the cause is simple and treatable. Sometimes a period problem is the first sign of a hormone condition that matters for long-term health or fertility. Knowing which tests are useful saves you from repeated, unnecessary “hormone panels”.

What counts as an irregular period?

A typical cycle, counted from the first day of one period to the first day of the next, is between 21 and 35 days. It is normal for it to vary by a few days. Your periods may be considered irregular if:

• cycles are often shorter than 21 days or longer than 35 days
• you have fewer than eight periods a year
• the length changes widely from month to month
• periods stop for three months or more (called secondary amenorrhoea)
• periods have not started by the age of 15 (primary amenorrhoea)

In the first two or three years after periods begin, and in the years before menopause, some irregularity is normal.

What are the common hormonal causes?

• PCOS, the most common cause in young women. Read what is PCOS.
• Thyroid problems, both underactive and overactive.
• High prolactin, from medicines, a small pituitary growth or other causes.
• Hypothalamic amenorrhoea, when the brain switches off the cycle because of low body weight, heavy exercise, under-eating or major stress.
• Premature ovarian insufficiency, when the ovaries stop working normally before the age of 40.
• Non-classic congenital adrenal hyperplasia, an inherited adrenal condition that can look like PCOS.
• Perimenopause, the years leading up to menopause. Read menopause symptoms and hormone therapy.

Non-hormonal causes matter too, including pregnancy, breastfeeding, fibroids, polyps, weight change, and some medicines, including hormonal contraceptives.

In a national ICMR study of Indian women aged 18 to 40, irregular ovulation, signs of high male hormones and mildly underactive thyroid were each common. So testing has to be targeted rather than one-size-fits-all.

Which tests are usually done first?

• Pregnancy test (urine or blood beta-hCG), always first if periods are late.
• TSH, with free T4 if needed. Read the thyroid function test explained.
• Prolactin. Stress, a difficult blood draw and some medicines can raise it mildly, so a high result is often repeated before further tests.
• FSH and LH with oestradiol, which help separate ovarian, pituitary and brain causes. A clearly raised FSH, together with periods that have been missing or very infrequent for several months before the age of 40, suggests premature ovarian insufficiency. Your doctor may repeat the test if the result is borderline or unexpected.

When are other tests added?

• Testosterone with SHBG, if you have acne, extra hair or suspected PCOS. Accurate lab methods matter. Read how PCOS is diagnosed.
• 17-hydroxyprogesterone, usually taken early in the morning in the first part of the cycle, to check for adrenal hyperplasia.
• DHEAS, and sometimes further tests, if male hormones are very high or rising quickly.
• AMH, which reflects the number of small follicles in the ovary. It can support a PCOS diagnosis in adults, and helps with fertility planning, but it is not a standalone test for irregular periods and it does not predict exactly when you will get pregnant.
• Blood count and ferritin, if periods are heavy.
• Pelvic ultrasound, to look at the womb lining, fibroids and ovaries.
• MRI of the pituitary, only if prolactin is clearly high without another explanation.

Does the day of the cycle matter?

Sometimes. FSH, LH and oestradiol are usually checked on day 2 to 5 of a period, if you are having periods. If periods have stopped, they can be checked on any day. TSH, prolactin and AMH can generally be checked on any day. Progesterone, used to confirm ovulation, is checked about a week before the next expected period. If you are on the pill or other hormones, tell your doctor, because many results are affected.

What happens after the tests?

Treatment depends on the cause and your goals: regular periods, treating acne or hair, protecting bone and womb health, or getting pregnant. Very infrequent periods over a long time can lead to a thickened womb lining, so even if pregnancy is not a goal right now, your doctor may suggest treatment to protect the lining. If pregnancy is your goal, read can I get pregnant with PCOS.

What should I ask my doctor?

• Which tests do I need, and on which day of my cycle?
• Could my medicines, weight change or exercise be affecting my periods?
• Do I need treatment to protect my womb lining or bones?

For a hormone assessment, book a consultation.