Hello! In our last lesson, we explored the global prevalence of PCOS and saw firsthand how the choice of diagnostic criteria—specifically, the 1990 NIH versus the 2003 Rotterdam criteria—dramatically influences how many women are identified with the syndrome. This highlighted the critical importance of having a clear and consistent diagnostic framework.
Today, we will perform a deep dive into that framework. This lesson is dedicated to mastering the third learning outcome of this module: Explain the Rotterdam diagnostic criteria for PCOS in detail. As the most widely accepted standard worldwide, a thorough understanding of these criteria is fundamental to grasping the modern concept of PCOS. We will break down each of the three components, explaining what they mean, how they are assessed, and how they combine to form a diagnosis.
The Foundation: The "2 out of 3" Rule
The 2003 Rotterdam consensus meeting was a landmark event that broadened the definition of PCOS. It moved away from requiring both hyperandrogenism and irregular cycles (the stricter NIH criteria) to a more flexible system.
The core principle of the Rotterdam criteria is that a diagnosis of PCOS can be made if a patient meets at least two out of the following three criteria, after other conditions have been ruled out:
- Oligo- and/or anovulation (infrequent ovulation or lack of ovulation, which usually presents as irregular menstrual cycles).
- Clinical and/or biochemical signs of hyperandrogenism (high levels of androgens, or male hormones, identified either by physical signs or by blood tests).
- Polycystic ovarian morphology (PCOM) on ultrasound (the presence of multiple small follicles in the ovaries).
This "2 out of 3" rule is elegantly captured in the following Venn diagram.
An Essential First Step: Diagnosis of Exclusion
Before applying the Rotterdam criteria, it is crucial to understand that PCOS is a diagnosis of exclusion. This means a clinician must first rule out other medical conditions that can cause similar signs and symptoms, such as irregular periods or excess androgen.
Polycystic Ovary Syndrome (PCOS) | Overview of Associated Conditions, Diagnosis & Treatments
The video 'Polycystic Ovary Syndrome (PCOS) | Overview' by JJ Medicine provides an excellent summary of the conditions that must be excluded before a PCOS diagnosis can be confirmed.
Watch the segment from 08:06 to 11:56. Pay close attention to the list of conditions that can mimic PCOS and the tests used to rule them out, such as those for thyroid disease, high prolactin levels, and congenital adrenal hyperplasia.
As the video explains, key conditions to exclude include:
- Thyroid dysfunction
- Hyperprolactinemia (high levels of the hormone prolactin)
- Non-classical congenital adrenal hyperplasia (NCCAH)
- Androgen-secreting tumors
- Cushing's syndrome
Only after these other possibilities have been investigated and ruled out can a clinician confidently apply the Rotterdam criteria.
Criterion 1: Oligo- and/or Anovulation
This criterion refers to irregular or absent ovulation. In clinical practice, this is most often identified through a patient's menstrual history.
- Oligomenorrhea: Infrequent menstrual periods.
- Amenorrhea: Absence of menstrual periods.
The precise definition of an "irregular" cycle varies with a woman's reproductive age, as the menstrual cycle naturally takes time to regulate after puberty.
The 2023 International Evidence-Based Guideline provides the most current and specific definitions for irregular cycles. Please read the section that details these definitions.
In the linked document, find the table and look for section 1.1 Irregular cycles and ovulatory dysfunction. Read recommendation 1.1.1, which provides exact cycle lengths that define irregularity based on the time since a woman's first period (menarche).
To summarize these crucial definitions for an adult woman (3 years post-menarche to perimenopause), irregular cycles are defined as:
- Cycles shorter than 21 days or longer than 35 days.
- Fewer than 8 cycles per year.
It's important to note that a woman can have regular monthly bleeding but still not be ovulating (anovulatory cycles). If there is suspicion, a clinician can confirm ovulation by measuring the serum progesterone level in the mid-luteal phase of the cycle.
Criterion 2: Hyperandrogenism (Clinical and/or Biochemical)
This criterion refers to an excess of androgens. It can be identified in two ways: through clinical signs (what can be seen on the body) or through biochemical tests (what is measured in the blood). A patient only needs to have one of these to meet this criterion.
Clinical Hyperandrogenism
These are the physical manifestations of high androgen levels. The most common sign is hirsutism—the growth of coarse, dark, terminal hair in a male-like pattern (e.g., on the face, chest, and back).
Other, less specific signs include:
- Acne, particularly when it is severe or persists past adolescence.
- Androgenic alopecia, which is female-pattern hair loss, typically a thinning of hair on the crown of the head.
Clinically, hirsutism is assessed using the Modified Ferriman-Gallwey (mFG) score, a standardized system that grades hair growth in nine different body areas.
Biochemical Hyperandrogenism
This involves measuring androgen levels in the blood. The most important tests are for testosterone.
Current Guidelines for Diagnosing PCOS - PMC
The review article 'Current Guidelines for Diagnosing PCOS' provides an excellent, in-depth explanation of how androgen excess is evaluated. This will give you the detailed theoretical knowledge you're looking for.
Please read section 3. Androgen Excess, including subsections 3.1. Hyperandrogenemia and 3.3. Clinical Hyperandrogenism. Focus on: The difference between total testosterone and free testosterone. The role of Sex Hormone-Binding Globulin (SHBG). The other androgens that can be measured (DHEAS and ANSD). The use of the mFG score and why the threshold can vary.
Key points from the reading include:
- Total vs. Free Testosterone: Most testosterone in the blood is bound to proteins, primarily SHBG. Only the unbound, or "free," testosterone is biologically active. In PCOS, SHBG levels are often low, which means that even if total testosterone is normal, free testosterone can be elevated. This makes measuring free testosterone (or a calculated value like the Free Androgen Index) a very sensitive marker for hyperandrogenism.
- Other Androgens: If testosterone levels are normal, doctors may measure other androgens like androstenedione (ANSD) and dehydroepiandrosterone sulfate (DHEAS). DHEAS is produced almost exclusively by the adrenal glands, so its elevation can point towards an adrenal source of androgens.
- mFG Score Threshold: A score of ≥8 was traditionally used to define hirsutism, but recent guidelines suggest a lower threshold of ≥4 to ≥6 may be more appropriate, depending on the patient's ethnicity, as baseline hair growth patterns vary.
Criterion 3: Polycystic Ovarian Morphology (PCOM)
This criterion is based on the appearance of the ovaries on a pelvic ultrasound, preferably a transvaginal ultrasound for better resolution.
The term "polycystic" is a bit of a misnomer. The "cysts" are not true cysts but rather small, immature follicles that have been arrested in their development. This gives the ovary a characteristic appearance.
The specific criteria for PCOM have evolved as ultrasound technology has improved.
Poly Cystic Ovarian Syndrome (PCOS) / Stein–Leventhal syndrome / Hyperandrogenic anovulation
First, let's watch a short, simple explanation of this criterion from the video 'Poly Cystic Ovarian Syndrome (PCOS)' by Dr. G Bhanu Prakash.
Watch from 03:34 to 04:19. He describes the ultrasound findings and the classic 'string of pearls' sign.
For a more detailed and up-to-date definition, let's turn back to the guideline paper.
Current Guidelines for Diagnosing PCOS - PMC
The 'Current Guidelines for Diagnosing PCOS' paper details the modern criteria for PCOM and explains how they have changed over time.
Please read section 5. Ovarian Morphology and the 'Current Recommendation' at the end of that section. Pay close attention to the specific numbers for follicle count and ovarian volume.
According to the latest international guidelines (from 2018 and reaffirmed in 2023), PCOM is defined by the presence of either of the following in at least one ovary:
- A follicle number per ovary (FNPO) of ≥ 20.
- An ovarian volume (OV) of ≥ 10 cm³ (or 10 ml).
It is important to note that if a woman already meets the criteria for irregular cycles and hyperandrogenism, an ultrasound is not strictly necessary to make the diagnosis of PCOS.
Test your understanding!
A 25-year-old woman has regular menstrual cycles every 30 days. Her blood tests are normal, including total and free testosterone. However, an ultrasound shows 25 follicles in her right ovary and an ovarian volume of 12 cm³.
Does she meet the Rotterdam criteria for a PCOS diagnosis? Why or why not?
Show answer
No, she does not meet the criteria for a PCOS diagnosis.
She only fulfills one of the three criteria: Polycystic Ovarian Morphology (PCOM) on ultrasound. Her cycles are regular (meeting neither oligomenorrhea nor amenorrhea), and her blood tests show no evidence of biochemical hyperandrogenism. The Rotterdam criteria require at least two of the three features for a diagnosis. The presence of PCOM alone is not sufficient.
Conclusion
Mastering the Rotterdam criteria is essential for understanding how PCOS is diagnosed in modern medicine. These criteria acknowledge that PCOS is a heterogeneous syndrome, meaning it can present in different ways in different women.
Key Takeaways:
- PCOS is a diagnosis of exclusion, meaning other conditions must be ruled out first.
- The Rotterdam criteria require a patient to meet at least two of three conditions:
- Oligo-/anovulation: Defined as irregular cycles (e.g., >35 days apart or <8 cycles/year in adults).
- Hyperandrogenism: Can be clinical (hirsutism, acne, alopecia) or biochemical (elevated free or total testosterone).
- Polycystic Ovarian Morphology (PCOM): Defined by ultrasound as ≥20 follicles per ovary or an ovarian volume ≥10 cm³.
- Each criterion has specific, evidence-based definitions that are crucial for accurate diagnosis.
Preview of the Next Lesson:
While the Rotterdam criteria are the most common, they are not the only ones. In our next lesson, we will compare the Rotterdam criteria with the NIH and Androgen Excess & PCOS Society (AE-PCOS) criteria. This will help you understand the nuances between different diagnostic approaches and appreciate the ongoing expert debate about how best to define this complex syndrome.