When understanding how LH works, you must know that its levels remain steady during your cycle and for the most part of every month.
They however jump up right before you ovulate. The period when there is a sudden surge in LH is the follicular phase of your menstrual cycle.
The follicular phase lasts between the first day of menstruation and the day of ovulation.
During this phase, the ovarian follicles, which contain the egg, grow bigger, and the egg matures for release.
Thanks to the high level of LH, one of these follicles releases the mature egg during your cycle. This is what causes ovulation. That released egg advances down your fallopian tube for fertilization.
If there is a sperm nearby to fertilize it within 24 hours, it will move into your womb, where it attaches and develops into a fetus. If this doesn’t happen, “lady red” (aka your period) comes visiting once again.