How is PCOS diagnosed? Tests, ultrasound and AMH explained

Many women in India are told they have PCOS after a single ultrasound showing “multiple follicles” or “polycystic ovaries”. That is not how the diagnosis should be made. PCOS (now also called PMOS) is a clinical diagnosis, based on a pattern of symptoms and tests, after other conditions have been ruled out. For background on the condition, read what is PCOS.

What criteria do doctors use?

The 2023 International Evidence-based Guideline, which the 2026 renaming did not change, builds on the Rotterdam criteria. In adults, PCOS is diagnosed when at least two of these three are present:

1. Irregular periods or ovulation problems. After the first three years from your first period, cycles shorter than 21 days or longer than 35 days, or fewer than eight periods a year, count as irregular. Any cycle longer than 90 days also counts.
2. Signs of high male hormones (hyperandrogenism). This can be clinical, such as excess facial or body hair, acne or scalp hair thinning, or biochemical, meaning raised male hormones on a blood test.
3. Polycystic ovaries on ultrasound, or a high AMH blood test.

And importantly, other causes must be excluded first.

If you have both irregular periods and signs of high male hormones, you do not need an ultrasound or AMH to make the diagnosis.

Which blood tests are usually done?

Your doctor will choose tests based on your symptoms. Commonly:

• testosterone with SHBG, from which a free androgen index or free testosterone is calculated. Accurate methods matter, because many routine testosterone tests are not reliable at the low levels seen in women.
• TSH, because thyroid problems can cause irregular periods. Read the thyroid function test explained.
• prolactin, because a high level can stop periods
• 17-hydroxyprogesterone, to check for a related adrenal condition called non-classic congenital adrenal hyperplasia
• FSH and oestradiol, especially if periods have stopped, to check for early menopause
• a pregnancy test if periods have stopped

These help rule out conditions that look like PCOS. Read irregular periods: which hormone tests are needed.

The guideline also advises checking metabolic health once PCOS is diagnosed, such as an HbA1c or glucose tolerance test, cholesterol, blood pressure and weight. Read PCOS, weight and metabolic health.

When does ultrasound help?

In adults, a transvaginal ultrasound (through the vagina) with a modern probe is the most accurate. The 2023 guideline counts the ovary as polycystic when it shows 20 or more small follicles, or has an enlarged volume. Abdominal scans are less accurate and should not be used alone to label PCOS, especially if you have never been sexually active.

Ultrasound is not used to diagnose PCOS in girls within eight years of their first period, because many healthy teenagers have ovaries with lots of follicles.

What about AMH?

AMH (anti-Müllerian hormone) is made by the small follicles in the ovary, so it is often high in PCOS. The 2023 guideline allows AMH to be used instead of ultrasound in adults. It should not be used on its own to diagnose PCOS, and it should not be used in adolescents. Different labs use different methods and cut-offs, so interpret results with your doctor.

How is PCOS diagnosed in teenagers?

Diagnosing PCOS in adolescents needs extra care. Irregular periods are normal in the first year or two after the first period, and acne is very common in teenage years. The international recommendations for adolescents, published in 2025, say that:

• both irregular periods (using age-specific definitions) and signs of high male hormones are needed
• ultrasound and AMH should not be used
• girls with some features who do not meet the criteria can be considered “at increased risk”, with lifestyle support and a reassessment later, often around full maturity or eight years after the first period

This matters in India, where acne, mild extra hair and irregular early cycles are very common in teenage girls, and where pelvic ultrasounds are easily done. A large Indian study found that many women had only one feature, such as polycystic-looking ovaries alone, which by itself is not PCOS. A label given too early can cause unnecessary worry about fertility and marriage. On the other hand, a girl with genuine features deserves support and follow-up rather than dismissal.

Is excess hair judged the same way in everyone?

No. The amount of body hair considered normal varies between ethnic groups, and South Asian women may naturally have more hair than some other groups. Doctors use a scoring chart (the modified Ferriman-Gallwey score), but the cut-off should take ethnicity into account. What matters is a change from your own normal and how much it bothers you.

What should I ask my doctor?

• Which of the criteria do I meet?
• Have other causes, such as thyroid, prolactin or adrenal problems, been ruled out?
• Do I need an ultrasound or AMH, or is it not necessary in my case?
• If I am a teenager, should we wait and reassess?

For a careful assessment, book a consultation.