From Dawn Stacey M.Ed, LMHC,
Your Guide to Contraception.
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About.com Health's Disease and Condition content is reviewed by Meredith Shur, MD

A.

Hormonal contraceptives either supply a steady level of both progestin (a substitute for progesterone) and estrogen every day or just progestin. This results in:

• No signal to a female's hypothalamus to release GnRH
• So there is never a signal to the pituitary gland to produce FSH
• This means that nothing will trigger the LH surge

Recap:

• The FSH signals the growth of egg follicles in the ovaries
• The LH triggers ovulation
• The ovary becomes relatively inactive without these hormones present

The result:

• No mature egg is produced or released.

Hormonal contraception keeps a woman's reproductive system in the same phase of her cycle on a continuous basis (by continuously skipping the release of GnRH, which triggers whole process of egg maturation)

The bottom line:

It basically comes down to the fact that hormonal contraceptives work by suppressing the two key hormones that are involved in ovulation

• The follicle stimulating hormone (which signals the growth of the egg)
• The luteinizing hormone (which triggers the egg’s release)

  These two hormones begin production when the body notices a shortage of estrogen and progesterone. Hormonal birth control provides just enough of these hormones to prevent the stimulation of FSH and LH production. Keeping estrogen and progesterone levels constant produces constant levels of FSH and LH, which keeps eggs from ripening and being released.

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