Research / Irregular cycles & PCOS — now PMOS

Our research

Irregular cycles & PCOS — now PMOS

In May 2026, the condition long known as polycystic ovary syndrome (PCOS) was formally renamed. Little Greenhouse's irregular-cycle tracking was already built on the diagnostic criteria behind both names — here's what's different now.

Name change: As of May 2026, PCOS is officially PMOS — Polyendocrine Metabolic Ovarian Syndrome. Both names are in use during a three-year transition period, and an existing PCOS diagnosis is still valid under the new name.

Why the name changed

“Polycystic ovary syndrome” implied the problem was ovarian cysts. It isn't — people with the condition don't have a higher rate of abnormal ovarian cysts than people without it. The follicles sometimes seen on ultrasound are a result of disrupted ovulation, not the cause of the condition. PMOS instead names what the condition actually is: a multisystem hormonal and metabolic condition affecting weight, mental health, skin, and the reproductive system, not just the ovaries.

How the rename happened

The new name followed a 14-year global process led by Professor Helena Teede (Monash Centre for Health Research & Implementation) and Professor Terhi Piltonen (Oulu University Hospital, Finland), with 56 patient and professional organizations and over 22,000 survey responses from patients and clinicians worldwide. It was published in The Lancet in May 2026.

The 21–35 day threshold

A cycle shorter than 21 days or longer than 35 is flagged as a PMOS-consistent pattern, directly from the Rotterdam Criteria used in clinical diagnosis — unchanged by the rename, since the underlying diagnostic criteria are the same condition under a new name.

Still current in 2023

This threshold was reaffirmed in the most recent international evidence-based PCOS/PMOS guideline, not an older figure left unreviewed. Full implementation of the new name is expected in the 2028 update to that guideline.

Common questions

Is PMOS a different condition from PCOS?

No — it's the same condition, same Rotterdam diagnostic criteria, new name. If you were diagnosed with PCOS, that diagnosis still stands under PMOS.

Why does Little Greenhouse use both names?

The rename is still in its three-year transition period, and most people searching for information are still using “PCOS.” The app and this page use both names together so nothing gets lost in the switch.

How common is PMOS?

It affects an estimated 1 in 8 women of reproductive age worldwide — around 170 million people — making it the most common hormonal disorder in that population.

References
  1. Teede H, Piltonen T, et al. The renaming of polycystic ovary syndrome to polyendocrine metabolic ovarian syndrome. The Lancet, May 2026.
  2. RANZCOG. RANZCOG Welcomes PCOS Renaming to PMOS, May 2026. ranzcog.edu.au
  3. Society for Endocrinology. Polyendocrine Metabolic Ovarian Syndrome (PMOS) is the new name for PCOS, May 2026. endocrinology.org
  4. Rotterdam ESHRE/ASRM-Sponsored PCOS Consensus (2003, revised 2023), summarized via AAFP
  5. International Evidence-based Guideline for the Assessment and Management of Polycystic Ovary Syndrome, 2023.
  6. Monash Centre for Health Research and Implementation. PMOS research program and diagnostic criteria, re-checked Oct 2026 — confirms Rotterdam Criteria unchanged, anchored to the 2023 International Guideline pending the 2028 update. monash.edu

See how Irregular cycles tracking actually works in the app

Little Greenhouse is still finishing its way to Google Play.

Get notified at launch