• Deep in the brain, the hypothalamus – a gland about the size of an almond which helps regulate a number of metabolic processes including hunger, thirst and body temperature – secretes gonadotropin-releasing hormone (GnRH).
• This stimulates the pituitary, a pea-sized gland at the base of the brain, to secrete follicle stimulating hormone (FSH).
• In the ovary, the follicles (sacs containing immature egg cells) respond by swelling, although one dominates the others and inhibits them from further development.
• The pituitary then decreases FSH production and releases luteinizing hormone (LH), which in turn signals the dominant follicle to release its egg.

If all goes well, a mature egg will be released from its follicle about 36 hours after the LH surge, beginning its journey into the uterus. If the body does not produce these hormones in exactly the right way, a hormonal imbalance or deficiency can cause infertility. Treatment with gonadotropins or "fertility drugs" can increase the likelihood of conception by stimulating inactive ovaries to ovulate or produce more than one egg at a time.