Introduction
Polycystic Ovary Syndrome (PCOS) is a common endocrine disorder affecting millions in the UK, with significant implications for metabolic, reproductive, and psychological health. For clinicians, navigating the management of PCOS is guided by two principal UK bodies: the National Institute for Health and Care Excellence (NICE) and the Royal College of Obstetricians and Gynaecologists (RCOG). While their overarching goals align, nuanced differences in their guidance can impact clinical practice. This comparison examines the NICE guideline (NG101, updated 2023) and the RCOG Green-top Guideline (No. 33, 2022) to highlight these distinctions and provide practical takeaways for 2025.
See how this translates to practice: Explore our Clinical governance features, visit the Patient Safety Hub, or review Clinical Safety & Assurance for enterprise rollout.
Diagnosis and Assessment
NICE Guideline NG101
NICE adopts the Rotterdam criteria, requiring the presence of two out of three features for diagnosis, after the exclusion of other pathologies:
- Ovulatory dysfunction: Oligo-anovulation.
- Hyperandrogenism: Clinical (hirsutism, acne) and/or biochemical.
- Polycystic ovaries on ultrasound: Defined as ≥20 follicles per ovary and/or an ovarian volume ≥10 ml.
Practical Takeaway: NICE is explicit that ultrasound is not required for diagnosis if the first two criteria are met, particularly in women over 40 years of age where ultrasound may be less reliable. Assessment should include screening for anxiety and depression, and a fasting lipid profile.
RCOG Green-top Guideline No. 33
RCOG also endorses the Rotterdam criteria but places a stronger emphasis on the specific phenotypes that result. It provides more detailed guidance on the assessment of long-term metabolic risks.
- Key Difference: RCOG dedicates significant detail to the interpretation of biochemical hyperandrogenism, advising the use of free androgen index (FAI) or calculated free testosterone where direct assays are unavailable.
- Assessment Focus: The guideline strongly emphasises baseline assessment of cardiovascular risk factors, including oral glucose tolerance test (OGTT) in high-risk individuals (e.g., BMI >30 kg/m², family history of diabetes), even if fasting glucose is normal.
Comparison Summary: Diagnosis
The diagnostic criteria are consistent. The key difference lies in emphasis: NICE provides a broader, more general practice-friendly algorithm, while RCOG offers deeper, specialist-level detail on biochemical assessment and long-risk risk stratification from the outset.
First-Line and Pharmacological Treatment
Lifestyle Modification
Both guidelines are unequivocal: lifestyle intervention is the first-line treatment for all overweight/obese women with PCOS. The target is a 5-10% reduction in body weight.
- NICE: Recommends a structured, multicomponent programme including diet, exercise, and behavioural strategies.
- RCOG: Echoes this but provides more specific commentary on dietary composition, suggesting a low-glycaemic index diet may offer advantages for improving insulin sensitivity.
Management of Metabolic Issues
- Metformin:
- NICE: Recommends considering Metformin for women with a BMI above 25 who have not responded to lifestyle changes, primarily for managing metabolic issues. Its use for infertility is secondary.
- RCOG: Positions Metformin more strongly, particularly for women with impaired glucose tolerance or diabetes, regardless of fertility desires. It is seen as a key agent for improving metabolic parameters.
- GLP-1 Receptor Agonists: This is a notable area of divergence.
- NICE: Does not include GLP-1 RAs within the PCOS guideline, as their use for weight management in PCOS falls outside the NG101 remit.
- RCOG: Acknowledges the emerging evidence and discusses that these agents may be considered for weight management in obese women with PCOS, in line with NICE technology appraisals for obesity (e.g., TA875). This makes RCOG's guidance more forward-looking on pharmacological weight management.
Management of Anovulation and Infertility
- First-line Ovulation Induction: Both guidelines recommend Letrozole as the first-line pharmacological agent for ovulation induction.
- Clomiphene Citrate: NICE and RCOG agree that Clomiphene is a second-line option if Letrozole is not tolerated or is unsuccessful.
- Monitoring: RCOG provides more detailed guidance on the monitoring of ovulation induction cycles, including the role of ultrasound follicular tracking.
Management of Hyperandrogenism
Both recommend the combined oral contraceptive pill (COCP) as first-line for managing menstrual irregularities and hyperandrogenism in women not seeking pregnancy. RCOG offers more detailed discussion on anti-androgenic progestins (e.g., co-cyprindiol, drospirenone).
Special Situations
Adolescents
Diagnosis in adolescents is challenging. Both guidelines advise caution.
- NICE: States that all three Rotterdam criteria must be present for diagnosis in adolescents under 18 years, including ultrasound findings (which require specialist paediatric ultrasound expertise).
- RCOG: Provides similar caution but offers more extensive discussion on the natural history of PCOS in adolescence and the importance of long-term follow-up.
Post-Pill PCOS
- NICE: Does not formally recognise "Post-Pill PCOS" as a distinct entity. It advises that symptoms emerging after stopping the COCP should be investigated as per standard diagnostic criteria after a suitable washout period.
- RCOG: Acknowledges the clinical scenario and recommends the same investigative approach as NICE, but provides more nuanced advice on reassuring patients that the COCP does not cause PCOS but rather unmask an underlying predisposition.
Preconception Care and Pregnancy
RCOG's guideline has a much stronger focus on this area, reflecting its obstetric remit. It provides detailed recommendations on optimising health pre-conception (screening for diabetes, recommending high-dose folic acid) and managing increased risks during pregnancy (gestational diabetes, pre-eclampsia). NICE covers this more briefly within its broader scope.
Practical Clinical Flow: A Synthesis for 2025
For a UK clinician, a pragmatic synthesis of both guidelines is recommended:
- Diagnosis: Use Rotterdam criteria (2/3). Avoid routine ultrasound in women >40 with clear anovulation and hyperandrogenism (per NICE). Use FAI for biochemical assessment where possible (per RCOG).
- Initial Assessment: Screen for anxiety/depression (NICE). Perform rigorous metabolic screening: consider OGTT if high-risk, even with normal fasting glucose (RCOG emphasis).
- First-line Treatment: Prescribe structured lifestyle intervention for weight loss (5-10%) for all overweight/obese patients. This is non-negotiable.
- Pharmacological Management:
- For Metabolism/Anovulation: Consider Metformin, especially if BMI >25 or with glucose intolerance (RCOG emphasis). For infertility, start with Letrozole.
- For Hyperandrogenism/Menstrual Regulation: Offer COCP (or Mirena for bleeding) if pregnancy not desired.
- For Weight Management: Be aware of the potential role for GLP-1 RAs in severe obesity, following NICE TA875, as highlighted by RCOG.
- Long-term Follow-up: Emphasise lifelong monitoring of metabolic health. Provide preconception counselling as a standard part of care for all women of reproductive age (RCOG emphasis).
Frequently Asked Questions (FAQs) for Clinicians
1. Which guideline should I prioritise in primary care?
Answer: NICE NG101 is generally more tailored to a primary care setting, providing a clear, stepped-care approach. However, integrating RCOG's emphasis on rigorous metabolic risk assessment (e.g., low threshold for OGTT) is highly recommended for comprehensive care.
2. Is an ultrasound always needed to diagnose PCOS in an adult?
Answer: No. According to NICE, if a woman has clear biochemical/clinical hyperandrogenism and oligo-anovulation, the diagnosis can be made without ultrasound. This is a key practical timesaver, especially in primary care.
3. What is the first-line drug for ovulation induction?
Answer: Both guidelines are clear: Letrozole is first-line. Clomiphene citrate is now second-line.
4. How should I manage a patient with PCOS and severe obesity who has failed lifestyle interventions?
Answer: Here, the RCOG guideline is more helpful. It signposts you to consider anti-obesity pharmacotherapy, such as GLP-1 receptor agonists, in line with NICE's broader obesity guidance (TA875), for which these patients may qualify.
5. What is the most critical aspect of long-term management?
Answer: Both guidelines agree that managing metabolic risk is paramount. This goes beyond fertility concerns and focuses on preventing type 2 diabetes and cardiovascular disease through regular screening and lifestyle promotion.
Source Links
- NICE Guideline NG101 (Last updated September 2023): Polycystic ovary syndrome: assessment and management
- RCOG Green-top Guideline No. 33 (Published December 2022): Long-term Consequences of Polycystic Ovary Syndrome