Luteinizing Hormone (LH)

Luteinizing hormone (LH) is a hormone produced by the pituitary gland at the base of the brain. The pituitary releases LH in pulses. LH has two main roles. A sharp rise in mid-cycle, the LH surge, triggers ovulation. After ovulation, LH maintains the corpus luteum, which produces progesterone.

Ovulation follows the start of the LH surge, but the interval varies. In a large study that timed ovulation directly at surgery, the median interval was 32 hours. Across individual women, the egg was released 24 to 56 hours after the surge began.¹ The timing also shifts from cycle to cycle. Home ovulation test kits detect this surge in urine. Many women use them to estimate the fertile window. A positive test does not prove ovulation. In LUF syndrome, the surge occurs, but the follicle never releases its egg. A follicle maturation study uses a series of ultrasounds to confirm that the follicle opened. An LH test cannot provide that confirmation.

Many RRM clinicians check basal LH early in the cycle, on day 2 or 3. A high LH-to-FSH ratio is one finding consistent with polyendocrine metabolic ovarian syndrome (PMOS), formerly polycystic ovary syndrome (PCOS). LH that stays high outside the surge window can point to a disturbance in hormone signals from the brain or to thyroid disease. A single LH value is difficult to interpret without a cycle chart to show its place in the cycle. Blood draws on random days lack that context. A chart shows the timing, so the result has meaning.

LH also matters in men. In men, LH pulses signal the Leydig cells of the testes to produce testosterone. When sperm count or sperm quality is abnormal, the evaluation of the male partner often includes LH, FSH, and testosterone.