How birth control methods prevent pregnancy

Birth control methods
Method How it prevents pregnancy

Hormonal

  • Prevents ovulation
  • Thickens mucus at the cervix so sperm cannot pass through
  • Changes the environment of the uterus and fallopian tubes to prevent fertilization and implantation should fertilization occur

Intrauterine device (IUD)

  • The progestin released by the levonorgestrel (LNg) IUD prevents fertilization by making the mucus in the cervix thick and sticky, so sperm can't get through to the uterus. The progestin and IUD change the uterine lining, preventing implantation in the rare case that fertilization occurs.
  • The copper in the copper IUD is toxic to sperm. It causes changes in the uterus and fallopian tubes that kill sperm. The IUD changes the uterine lining, which prevents implantation in the rare case that fertilization occurs.

Barrier methods

  • Block sperm from reaching the egg
  • Some are used with spermicides, which kill sperm.

Fertility awareness (natural family planning)

  • Identifies the time during a woman's cycle when she is most likely to become pregnant (fertile). An additional method or abstinence should be used during this time of fertility.

Permanent birth control (sterilization)

Last Updated: May 22, 2008

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