Abnormalities
Ovulatory disorders
3 min read
This is where the cycle-versus-period distinction becomes practical. If ovulation does not happen, there is no corpus luteum; without a corpus luteum there is no progesterone; without progesterone the endometrium keeps thickening under unopposed estrogen until it breaks down unpredictably. The result is bleeding at random intervals, sometimes very heavy, sometimes absent for months — and, over years, an increased risk of endometrial hyperplasia.
The distinction that most sources skip. Bleeding in an anovulatory cycle is not a period. A period is progesterone withdrawal bleeding, and without ovulation there is no progesterone to withdraw. What happens instead is either estrogen breakthrough bleeding — the lining proliferating under unopposed estrogen until it outgrows its support and breaks down — or estrogen withdrawal bleeding, when a follicle develops, fails to ovulate, and then regresses.
This is not pedantry. It is the reason anovulatory bleeding is unpredictable in timing rather than merely irregular, the reason it can be far heavier than a true period, and the reason chronic anovulation carries a hyperplasia risk that ordinary heavy periods do not. Calling both of them "periods" hides all three facts.
FIGO replaced the fifty-year-old WHO classification in 2022 with a system organised by anatomical level, remembered as HyPO-P.
| Type | Level | Typical examples |
|---|---|---|
| Type I | Hypothalamic | Functional hypothalamic amenorrhea from energy deficit, excessive exercise or psychological stress; congenital GnRH deficiency; infiltrative or neoplastic lesions. |
| Type II | Pituitary | Hyperprolactinemia, including prolactinoma and drug-induced; other pituitary tumours; Sheehan syndrome. |
| Type III | Ovarian | Premature ovarian insufficiency; iatrogenic causes including chemotherapy, radiotherapy and surgery; genetic causes. |
| Type IV | PCOS | Kept separate because its pathophysiology is multifactorial and does not sit at one anatomical level. |
FIGO Ovulatory Disorders Classification System: Munro MG, Balen AH, Cho S, et al. Int J Gynecol Obstet. 2022;159(1):1–20. Types I–III are subclassified at a second level by the mnemonic GAIN-FIT-PIE (Genetic, Autoimmune, Iatrogenic, Neoplasm; Functional, Infectious and Inflammatory, Trauma and vascular; Physiological, Idiopathic, Endocrine).
Two that are commonly mislabelled
PCOS is diagnosed in adults by the Rotterdam framework as updated in the 2023 international guideline: two of three from clinical or biochemical hyperandrogenism, ovulatory dysfunction, and polycystic ovary morphology — with the 2023 change that AMH may now substitute for ultrasound in adults only. Where irregular cycles and hyperandrogenism are both present, neither ultrasound nor AMH is needed. In adolescents both hyperandrogenism and ovulatory dysfunction are required, and neither ultrasound nor AMH should be used, because normal pubertal physiology overlaps too heavily; morphology is not assessed until eight years past menarche.
Premature ovarian insufficiency is not early menopause, and the distinction is not pedantic — ovarian function in POI fluctuates and can return intermittently, so spontaneous ovulation and pregnancy remain possible. ESHRE criteria are oligomenorrhea or amenorrhea for at least four months before age 40, with FSH above 25 IU/L on two occasions more than four weeks apart. Note the threshold divergence: NICE uses 30 IU/L and the older POF literature 40 IU/L; ESHRE's lower cut-off is intended to capture autoimmune cases that present with less markedly elevated FSH.
About FSH tests. A single blood test is a poor way to answer "am I in perimenopause." FSH swings widely from cycle to cycle during the transition, so a normal result does not rule it out and a high one does not confirm it. Your pattern of cycles over time is the better evidence — which is what the staging tool on this site uses.
On FSH in the transition. Cycle-to-cycle FSH variability across the menopausal transition limits the value of isolated measurement in women still menstruating; STRAW+10 stages on bleeding criteria for precisely this reason. Reserve FSH for the settings where it changes management — suspected POI, hysterectomy without oophorectomy, and ambiguity under age 45.