The female reproductive system includes the uterus, fallopian tubes, and ovaries. The ovaries are almond-shaped glands located on either side of the uterus. They produce the sex hormones estrogen and progesterone, which regulate a woman’s menstrual cycle.

In addition to producing hormones, the ovaries contain hundreds of thousands of eggs. Each month hormones stimulate the ovaries to develop mature eggs. Usually, only one of these eggs reaches maturity and is able to be ovulated and then fertilized. Fertilization can occur only during ovulation—the time in a woman’s menstrual cycle when the mature egg is released from the ovary and travels through the fallopian tube.

For conception to occur, one sperm must fertilize the mature egg while in the fallopian tube. A sign that fertilization has occurred is when the egg begins to cleave, or divide, into multiple cells forming a blastocyst. The blastocyst then travels down the fallopian tube and enters the uterus. Implantation of the blastocyst must occur within the lining of the uterus for the further development of an embryo.

The birth control patch is one method used to prevent pregnancy. The small square patch can be composed of several layers. The hormones estrogen and progestin (the synthetic form of progesterone), are usually located in the lower adhesive layer. This layer is placed directly on the skin, usually on the buttocks, stomach, or upper arm. It is considered a hormonal type of birth control, meaning that it delivers synthetic hormones into the bloodstream to interfere with a woman’s normal menstrual cycle.

These hormones prevent pregnancy by

A single patch can be worn for 1 week before it needs to be replaced. It should be replaced on the same day each week for 3 weeks in a row. The patch is not worn during the fourth week, at which time the woman will have her menstrual period.

The birth control patch is a prescription medication, and risks associated with its use are similar to those of oral birth control pills.