LH (Luteinizing Hormone)

LH surges from the pituitary gland at mid-cycle, triggering the dominant follicle to rupture and release its egg (ovulation) approximately 36 hours later. LH also stimulates testosterone production in men and supports the corpus luteum after ovulation to maintain progesterone output.

In fertility treatment, LH is detected by urinary predictor kits to time IUI and intercourse. Recombinant LH (or hCG, which mimics LH) is added to gonadotropin protocols when LH activity may be insufficient — particularly in long GnRH agonist protocols or in women with hypothalamic amenorrhea. Premature LH surges during stimulation can be prevented with GnRH antagonist or agonist co-treatment.