The FSH, LH and prolactin blood tests assess reproductive and pituitary function. FSH and LH evaluate ovarian reserve, menstrual irregularities, puberty timing, menopause and infertility in women and hypogonadism in men. Prolactin checks for pituitary causes (including hyperprolactinemia) of menstrual disturbances, galactorrhea or infertility. Results help diagnose amenorrhea, irregular cycles, infertility and guide further investigation or treatment.

FSH (follicle-stimulating hormone) and LH (luteinizing hormone) blood tests assess reproductive function. In women, FSH gauges ovarian reserve and menopausal status; LH evaluates ovulation and conditions like PCOS—timing matters (early-cycle FSH, midcycle LH surge). In men, they assess testicular function and sperm production. Results guide infertility evaluation and treatment planning.

A good FSH level on cycle day 3 is typically under about 10 mIU/mL (ideally ~3–9 mIU/mL). Day‑3 LH is usually around 2–12 mIU/mL. A roughly 1:1 LH:FSH ratio is favorable for conception; a ratio ≥2:1 often suggests PCOS. Persistently high FSH (over ~10–15 mIU/mL) may indicate diminished ovarian reserve and lower pregnancy chances—discuss results with your clinician.

No fasting is required for FSH, LH or prolactin blood tests. Prolactin is sensitive to stress, exercise, sleep and nipple stimulation, so samples are usually taken in the morning; rest 15–30 minutes before the draw and avoid heavy exercise or sexual activity beforehand. Tell your clinician about medications, pregnancy or recent procedures, as these can affect results and may need repeat testing.

The best time to test LH and FSH depends on the reason. For baseline ovarian reserve and fertility assessment, measure serum FSH and LH on cycle days 2–4 (commonly day 2–3). To detect ovulation, use a urine LH test around mid‑cycle to catch the surge (predicts ovulation 24–36 hours later). For men or non‑fertility reasons, blood tests can be done any time, preferably in the morning.

Infertility can occur when prolactin rises above the normal reference range (generally >20–25 ng/mL in women). Mild elevations may not always impair fertility, but levels above about 50 ng/mL commonly cause menstrual irregularities and anovulation. Very high concentrations (often >100 ng/mL) suggest a prolactinoma and carry a high risk of infertility; evaluation and treatment are recommended.