LH Surge

The LH surge is the pivotal hormonal event of the menstrual cycle. When the dominant follicle is mature, estradiol levels peak, signaling the pituitary to release a large pulse of LH. This surge triggers final maturation of the egg and causes the follicle wall to rupture and release the oocyte approximately 36–44 hours later.

At-home ovulation predictor kits (OPKs) detect LH in urine and are widely used to time intercourse, ICI, and IUI. A positive OPK indicates the surge has begun; IUI is typically scheduled for 24–36 hours later. Digital monitors and more sensitive kits can also detect the rise in estrogen that precedes the surge, giving additional lead time. In IVF, a premature LH surge is prevented using GnRH agonist or antagonist medications.