Hormone focus. A sharp rise in follicle-stimulating hormone followed by an increase in luteinizing hormone, also from the pituitary, stimulates one follicle to swell further and burst, releasing an egg into one of the fallopian tubes; that egg then travels to the uterus. Estrogen levels continue to increase, further thickening the uterine lining and supporting the growth of immune system cells in the uterus. Testosterone takes a quick surge and drops right around ovulation.
