In an anovulatory cycle the ovary does not release an egg. The uterine lining still builds up under estrogen and eventually sheds, so bleeding happens, but without the progesterone phase that follows true ovulation. The bleeding can be regular or irregular, light or heavy, and often passes for a normal period.
Why it matters
Without egg release, pregnancy cannot occur in that cycle. Occasional anovulation is common and normal; frequent anovulation is one of the most common treatable reasons for difficulty conceiving, and it is easily missed because regular bleeding gives false reassurance.
Common causes
PCOS is the most common cause in women of reproductive age. Thyroid disorders, high prolactin, significant stress, rapid weight change, and excessive exercise can also interrupt ovulation. It is also frequent in the first years after periods begin and in the years approaching menopause.
How it is diagnosed
A mid-luteal progesterone blood test (about a week before the expected period), ultrasound follicle tracking, or ovulation kits that never show a clear surge all help confirm whether ovulation is happening. Treatment is directed at the cause, and ovulation-inducing medication is available when needed.