Some contraceptive methods block ovulation, which is the release of an egg into the fallopian tube. Pregnancy cannot occur without the availability of an egg for fertilization. Forms of birth control that work in this way include oral contraceptives (birth control pills), vaginal rings, hormonal pellets that are inserted under the skin (contraceptive implants), and injected hormones.
Some contraceptive methods prevent sperm from reaching an egg. Condoms (both male and female), spermicides, diaphragm, cervical cap, the contraceptive sponge and the IUD work this way.
Inhibition of implantation, that is prevention of a fertilized egg from implanting in the uterine lining, is a minor effect compared to the other effects. New data show that even IUD effects, both copper and hormonal, are nearly all pre-fertilization, that is sperm do not reach the egg.
Emergency contraception is a form of birth control that can be used for back up birth control when other forms of birth control were absent or are suspected to have failed, for example following unprotected sex or if a condom broke. Emergency contraception consists of taking a hormone pill for a couple of days or inserting a copper IUD. The hormone pill option must be taken within 72 hours following sex. The IUD must be inserted within 5 days. These options work by stopping the sperm from joining the egg or stopping implantation.
For more information on contraceptive methods or reproductive health please visit the following sites:
- The website of the Office on Women’s Health in the Department of Health and Human Services — womenshealth.gov
- The website of the American College of Obstetricians and Gynecologists (ACOG) Resource Center — www.acog.org
- Mayo Clinic Birth Control Guide — www.mayoclinic.com/health/birth-control/BI99999
- Medline Plus (sponsored by NIH) – Birth Control — www.nlm.nih.gov/medlineplus/birthcontrol.html
- Planned Parenthood Website — www.plannedparenthood.org