Birth Control Shot (Medroxyprogesterone Injection)

MEDICAL ANIMATION TRANSCRIPT: A series of events called the menstrual cycle happens about once every month to prepare a woman's body for pregnancy. Changing levels of natural chemicals in the bloodstream called hormones control these events. The reproductive organs affected by these hormones include the vagina, cervix, uterus, fallopian tubes, and ovaries. The ovaries produce two main hormones called estrogen and progesterone. As the level of estrogen begins to rise, it causes the normally thick mucus inside the cervix to thin out. Estrogen also triggers other hormones to cause one of the ovaries to release an egg. This process is called ovulation. If a woman has sex during this time, a man's reproductive cells, called sperm, can pass through the thinner, more receptive mucus to fertilize an egg. In the uterus, estrogen has caused the lining to thicken, which has prepared it to receive a fertilized egg. Rising progesterone levels cause glands in the lining to make fluid that feeds the fertilized egg. Progesterone also causes the thinned-out mucus in the cervix to become thick again, which helps to prevent sperm from passing through. If an egg hasn't been fertilized or doesn't implant in the uterine lining, the levels of both estrogen and progesterone begin to fall. This drop in hormone levels causes menstruation, a process where the uterus sheds its inner tissue lining and blood through the cervix and into the vagina. If you don't want to get pregnant, you may decide to use a type of birth control. One type of birth control is the progestin shot. It prevents pregnancy for up to three months. You get the shot in the muscles of your upper arm or buttocks. If it's been more than 15 weeks since your last shot, you will need to use a backup method of birth control for the first week after getting your next shot. The shot contains a synthetic hormone similar to progesterone, called progestin. In high enough levels, progestin stops the ovaries from releasing eggs. When there is no egg available to fertilize, a woman can't get pregnant. Progestin also prevents pregnancy by keeping the mucus in the cervix thick enough so sperm can't get through it. A third way progestin prevents pregnancy involves its influence on the lining of the uterus. In contrast to natural progesterone, progestin is slightly different chemically. Over time, it makes the uterine lining thinner instead of thicker. As a result, if fertilization of an egg were to take place, the lining would likely be too thin for the fertilized egg to successfully implant in the uterus, so it would pass out of the body with the next menstrual period. Side effects of the birth control shot may include changes in your menstrual cycle, extra menstrual bleeding or spotting, loss of bone density, breast tenderness, weight gain, headaches, nervousness, and dizziness. If you get a birth control shot on time every three months, it's 99% effective at preventing pregnancy. This means about one out of one hundred women will become pregnant each year using this form of birth control, but with typical use, it's 94% effective at preventing pregnancy. This means about six out of one hundred women will become pregnant each year if they don't always get their shot on time. To find out more about the birth control shot, talk to your healthcare provider.