Estradiol (E2)
The main and most potent human estrogen. It drives the menstrual cycle, builds the uterine lining, protects bone and blood vessels, and its fall defines menopause. Levels swing enormously across the cycle, so timing the draw is everything.
What it measures
Estradiol is the principal estrogen produced by the ovaries in women of reproductive age, with smaller amounts from fat tissue and, in men, the testes and aromatisation of testosterone. It rises through the follicular phase as a follicle matures, peaks just before ovulation to trigger the LH surge, and is produced by the corpus luteum in the luteal phase. Because of this swing, a single value is only interpretable against the cycle day (or menopausal status). It is measured to work up absent or irregular periods, suspected menopause, fertility problems, delayed or precocious puberty, and — in men — gynaecomastia or low testosterone. In IVF it is tracked daily to monitor ovarian response.
What a high value can mean
- Ovulation approaching / mid-cycle peak — physiological, not pathological.
- Ovarian stimulation (IVF drugs) — expected; very high levels flag hyperstimulation risk.
- Estrogen-secreting ovarian tumour (granulosa cell) — rare; persistently high without a cycle explanation.
- Pregnancy — rises steadily.
- Obesity — fat tissue aromatises androgens to estradiol.
- In men — gynaecomastia, testicular tumour, cirrhosis, or excess aromatase.
What a low value can mean
- Menopause / perimenopause — the defining fall; high FSH + low estradiol.
- Primary ovarian insufficiency — menopause before 40.
- Hypothalamic amenorrhoea — low body fat, over-exercise, stress, eating disorder; low FSH/LH too.
- Hyperprolactinaemia — a high prolactin suppresses the axis.
- Turner syndrome / gonadal dysgenesis — congenital.
- GnRH-analogue treatment — deliberate suppression.
When to discuss with a doctor
Estradiol is almost never read alone — it is paired with FSH and LH to locate the problem at the ovary versus the pituitary/hypothalamus. High FSH + low estradiol in a woman over ~45 with irregular cycles confirms the menopausal transition; the same pattern under 40 means primary ovarian insufficiency and warrants gynaecology + endocrinology. Low FSH/LH + low estradiol points upstream to the hypothalamus (weight, stress, prolactin). Mediora.AI reports estradiol against your sex, cycle phase where known, and its companion hormones; the fertility or menopause decision belongs with your gynaecologist.