Missing Period: Causes of Amenorrhea and What the Workup Involves
What causes a missing period beyond pregnancy — hypothalamic amenorrhea, PCOS, POI, thyroid, prolactinoma — and how each is diagnosed.
No period for months isn't usually "just stress" — at least not reliably, and not as a complete answer. Amenorrhea has a real differential diagnosis, and the workup is well-defined. Here's what could be going on and how to find out.
What causes a missing period besides pregnancy?
The main causes of secondary amenorrhea (periods that stopped after being present) include: hypothalamic amenorrhea from low body weight, high exercise volume, or chronic underfueling; PCOS; premature ovarian insufficiency; thyroid dysfunction; prolactinoma (a benign pituitary adenoma); and medications including Depo-Provera, certain antipsychotics, and GLP-1s. Before any workup, pregnancy should always be ruled out first — that's step one regardless of circumstances.
What is amenorrhea?
Primary amenorrhea refers to never having had a period by age 15. Secondary amenorrhea is having had periods that then stopped for 3 or more months. The causes and workup differ between these two types, though they share some overlap. Secondary amenorrhea is more common and has a broader differential that includes reversible causes.
Can you get pregnant if you don't have a period?
It depends on the cause. If amenorrhea is from hypothalamic suppression (hypothalamic amenorrhea), restoring ovulation — through weight restoration, reducing exercise, or improving energy availability — can allow natural conception. If it's from PCOS, ovulation induction with medication is often effective. If it's from premature ovarian insufficiency, natural conception is much less likely but not impossible. The treatment and prognosis depend entirely on the underlying cause.
What is hypothalamic amenorrhea and how is it treated?
Hypothalamic amenorrhea (HA) is suppression of the hypothalamic-pituitary-ovarian axis due to low body weight, high training volume, chronic stress, or insufficient caloric intake. It's the most underdiagnosed cause of missing periods in reproductive-age people. FSH and LH are both low. It is often reversible — with weight restoration, reduced exercise load, and improved energy availability. Treatment targets the cause, not the period itself.
How does under-eating affect your period and fertility?
The hypothalamus requires adequate energy availability to signal the rest of the reproductive axis. When caloric intake is too low relative to energy expenditure — even in someone who doesn't appear underweight — the hypothalamus suppresses GnRH, which stops the hormonal cascade that triggers ovulation. This is a protective mechanism, not a malfunction. Restoration requires addressing the energy deficit.
Can over-exercising stop your period?
Yes. High training volume combined with insufficient caloric intake or very low body fat can suppress the reproductive axis in the same way as under-eating. Elite athletes and recreational athletes who train intensively are both at risk. The threshold varies by individual. A period that goes missing with increased training intensity and returns when training eases is a clear signal of exercise-related hypothalamic suppression.
What tests diagnose the cause of a missing period?
The workup order: rule out pregnancy first. Then: prolactin and TSH (rules out pituitary and thyroid causes). Then: FSH, LH, and estradiol (maps the hypothalamic-pituitary-ovarian axis). A pelvic ultrasound if structural abnormality is suspected. MRI of the pituitary if prolactin is elevated. The pattern of results across these tests points to the diagnosis.