Contraception
An intervention to prevent pregnancy. This can be achieved in many ways. The following classification describes various interventions, in order, from sperm formation to implantation of the fertilized ovum.
· Prevent sperm formation. There is no satisfactory way to do this yet.
· Keep sperm out of the semen by cutting, tying or otherwise blocking the spermatic ducts.
· Keep semen out of the vagina by abstinence, ejaculation outside the vagina, or by catching the semen in a condom.
· Keep semen out of the vagina when fertilization could occur by predicting when ovulation will take place, and abstaining from coitus for seven days before and 36 hours after that event, or by abstaining from the beginning of menstruation until after ovulation. This method is called periodic abstinence. The various methods of predicting ovulation are known as mucus, Billings, basal temperature and symptothermal methods.
· Kill sperm in the vagina by using spermicides.
· Prevent sperm from passing through the cervical canal by using a cervical barrier or by using hormones to change the cervical mucus so that it becomes impenetrable to sperm (the mini-pill).
· Prevent sperm from reaching the egg by cutting, tying or otherwise blocking the fallopian tubes, as in female sterilization.
· Prevent ovum formation by using hormones (pill or injection) to prevent egg maturation and release.
· Prevent implantation of a fertilized egg by using an IUD. This can also be done by post-coital administration of hormones (the morning-after pill).
