What is LH?

Alongside FSH, the other pituitary hormone acting on the ovary, LH brings an ovarian follicle, the fluid-filled sac that holds a developing egg, to maturity. Releasing the egg is a separate job, done by a single sharp surge of LH in the middle of the cycle.

FSH arrives in the same pulses and acts on the same follicle. Oestradiol comes from that follicle rather than from the pituitary, so a change in LH shows in oestradiol only once the ovary has responded.

How often the brain signals the pituitary sets how much LH comes out. Oestradiol from a developing follicle reaches the pituitary and alters how much LH follows.

Pulses arrive through the day, and in those who have a menstrual cycle a surge around ovulation lifts LH for a day or two. A single measurement may land on a pulse, on the surge, or between them, and the figure alone does not say which. What a yearly test can show is a change in pituitary output larger than any pulse or surge could account for. This is Do Health's monitoring schedule, not a general recommendation for everyone.