How do you prevent pregnancy?
Take birth control (pills, patch, ring, shot, etc), wear condoms, or practice abstinence. Avoid sex when you are ovulating.
The one method that works ALWAYS is not to have sexual intercourse. IF you are going to have intercourse, there are means of birth control that REDUCE the chances of becoming pregnant- nothing works EVERY time. Condoms (when worn and used correctly) are fairly effective. There are foam contraceptives, birth control pills, etc- and the rhythm method- not having intercourse during the period when you can get pregnant.
If you are in jovial mood and female keep away from Boys. If you are married and do not want babies. just swallow pills. Ask your male partner to wear a condom or you can use a diaphragm, insert spermicide gel into your vagina. or go for IUD, etc. Or keep your legs closed.
To be able to have sex without getting pregnant you need to use real contraceptives, and to use them right. Either go see a doctor, or buy yourself a packet of condoms.
You can prevent pregnancy by using a condom or birth control pills.
Condoms don't prevent pregnancy by killing sperm, they prevent pregnancy by capturing sperm cells when the man ejaculates. Once a man ejaculates in a woman's vagina without a condom there is nothing a condom can retroactively do to prevent pregnancy. Best to put on a condom before intercourse. If you have ejaculated in a woman the best way to prevent pregnancy is the "morning after pill". It's a dose of hormones that can prevent ovulation.
Once a pregnancy is established, no. The pills can only prevent pregnancy ( though they are not 100% effective) if given the time to saturate your bloodstream and taken daily to prevent pregnancy. Taking the pills, if you haven't been taking them to prevent pregnancy, will not cause a miscarriage. I suggest going to a doctor.