The Difference Between PCO and PCOS

The medical conditions PCO (Polycystic Ovaries) and PCOS (Polycystic Ovary Syndrome) are often conflated, leading to misunderstandings about their symptoms and management. With the recent renaming of PCOS to PMOS (Polyendocrine Metabolic Ovarian Syndrome), understanding the distinctions between all three terms has become even more relevant.

This guide aims to provide clarity on PCO, PCOS and the new PMOS designation, as well as practical strategies for managing each.

An important update: On 12 May 2026, an international consensus published in The Lancet renamed Polycystic Ovary Syndrome (PCOS) to Polyendocrine Metabolic Ovarian Syndrome (PMOS). The rename reflects a broader understanding of the condition's hormonal and metabolic nature beyond the ovaries alone. PCO (Polycystic Ovaries) remains a separate and distinct condition. Both PCOS and PMOS refer to the same syndrome — the name is changing, not the diagnosis. Read our explainer on what the rename means for your hormones and fertility.

What is PCO (Polycystic Ovaries)?

Polycystic Ovaries (PCO) refers to the presence of multiple small follicles in the ovaries, generally identified through an ultrasound. The term describes an anatomical finding rather than a medical syndrome. Women with PCO may not experience any symptoms, hormonal imbalances or fertility difficulties — the ovaries simply appear to have more follicles than average.

PCO is relatively common, estimated to affect around 20 to 30% of women of reproductive age. Having PCO does not automatically mean a woman has PCOS (PMOS), and many women with PCO conceive without difficulty and without any medical intervention.

What is PCOS (now also known as PMOS)?

Polycystic Ovary Syndrome (PCOS), now being renamed Polyendocrine Metabolic Ovarian Syndrome (PMOS), is a hormonal and metabolic disorder that goes significantly further than the anatomical finding of polycystic ovaries. It is characterised by a combination of symptoms including irregular or absent menstrual cycles, elevated androgen levels, insulin resistance, and often (though not always) polycystic ovaries on ultrasound.

PCOS (PMOS) affects around 1 in 10 women of reproductive age in the UK and is one of the most common causes of fertility difficulties. The new name, PMOS, was chosen to better reflect the condition's wider metabolic and endocrine effects, including its impact on insulin regulation, inflammation and hormonal signalling beyond the ovaries alone.

The core differences between PCO and PCOS (PMOS)

The key distinction is that PCO is a structural finding with no necessary symptoms or health consequences, while PCOS (PMOS) is a systemic syndrome with hormonal, metabolic and reproductive implications. A woman can have PCO without PCOS (PMOS), but most women diagnosed with PCOS (PMOS) will also have polycystic ovaries on ultrasound.

The table below summarises the key differences:

Strategies for managing PCOS (PMOS)

Medications

Several types of medications may be used to address the various aspects of PCOS (PMOS):

• Metformin: Commonly prescribed to help manage insulin resistance and support weight regulation. The NHS recommends it as part of PCOS management for eligible women.
• Clomifene citrate or letrozole: Fertility medications that may be used to stimulate more regular ovulation in women with PCOS (PMOS) who are trying to conceive.

Hormonal interventions

• Oral contraceptives: May help regulate hormones and normalise menstrual cycles in women with PCOS (PMOS) who are not trying to conceive.
• Hormone therapy: May be relevant for some women managing ongoing hormonal symptoms.

Diet

Diet plays an important role in managing PCOS (PMOS), particularly given its impact on insulin resistance, which is now central to the PMOS designation:

• Low glycaemic index foods: Whole grains, lentils and oats may help support more stable insulin levels.
• Lean proteins: Including fish, turkey and legumes may support weight management and hormonal balance.
• High fibre foods: Vegetables, fruits and legumes may help support insulin sensitivity.

Lifestyle modifications

• Regular exercise: Moderate cardiovascular and strength training exercise may support weight management, insulin sensitivity and fertility in women with PCOS (PMOS).
• Stress management: Techniques such as mindfulness and yoga may help reduce cortisol levels, supporting hormonal balance.

Nutritional supplements

Several supplements have evidence suggesting they may support the management of PCOS (PMOS) symptoms:

• Inositol and Folate: Myo-inositol may support egg health, more regular ovulation and insulin sensitivity in women with PCOS (PMOS). Paired with bioavailable folate, it addresses two of the key nutritional priorities for PCOS-related fertility.
• N-Acetyl Cysteine (NAC): Research suggests NAC may improve insulin sensitivity and has anti-inflammatory properties that may help reduce systemic inflammation associated with PCOS (PMOS).
• Psyllium Husk: May help support insulin sensitivity. Insulin resistance in PCOS (PMOS) may contribute to excess androgen production, so supporting blood sugar regulation is relevant across multiple symptoms.
• Omega-3 fatty acids: The anti-inflammatory properties of omega-3s may help reduce systemic inflammation associated with PCOS (PMOS). Research also suggests omega-3s may support insulin sensitivity and hormonal balance.

Zita West PCOS (PMOS) Support Pack

Brings together the key supplements discussed above — inositol and folate, NAC, omega-3, psyllium husk, Femceive probiotic and vitamin D — in a single pack formulated for women with PCOS (PMOS). Each ingredient addresses a mechanism that research suggests may be relevant to managing the condition.

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FAQs: PCO, PCOS and PMOS

What is the difference between PCO and PCOS?

PCO (Polycystic Ovaries) is a structural finding on ultrasound showing multiple small follicles in the ovaries. It does not necessarily cause symptoms or hormonal imbalance. PCOS (Polycystic Ovary Syndrome) is a hormonal and metabolic syndrome that includes irregular cycles, elevated androgens and insulin resistance, and may or may not involve polycystic ovaries on ultrasound.

Can you have PCO without PCOS (PMOS)?

Yes. Many women have polycystic ovaries on ultrasound without meeting the diagnostic criteria for PCOS (PMOS). PCO without PCOS does not generally require treatment and may have no impact on fertility or overall health.

Does PCO affect fertility?

PCO alone does not typically affect fertility. Women with PCO but without PCOS (PMOS) usually ovulate regularly and conceive without difficulty. If fertility issues are present alongside PCO, further investigation may be needed to determine whether other factors are involved.

What supplements may help with PCOS (PMOS)?

Research suggests that myo-inositol, NAC, omega-3 fatty acids, psyllium husk and vitamin D may each support different aspects of PCOS (PMOS) management, including insulin sensitivity, inflammation and hormonal balance. The Zita West PCOS Support Pack brings these together in one place. If you would like personalised guidance, book a free 1:1 fertility product consultation with our team.

External references: NHS: Polycystic ovary syndrome (PCOS)  |  The Lancet: PMOS consensus 2026

This content is for educational purposes only and is not intended to diagnose, treat, or replace medical advice. Always consult your healthcare provider for diagnosis and appropriate treatment options.