Taken from: http://parentingteens.about.com/cs/teenssex/l/blbcmyth.htm
Myth: The condom is a foolproof method of birth control.
Fact: The condom is not foolproof. It has a failure rate of 4 to 15 per hundred women. Failures occur because of improper and/or inconsistent use. Occasionally the condom itself is defective. If intercourse is commenced before the condom is put on, sperm may have already entered the vagina in the pre-ejaculatory penile lubricating fluid. Failure to withdraw shortly after ejaculation may cause the condom to slip off. The condom can also break during intercourse.
Myth: If I take a pill after intercourse I won’t get pregnant.
Fact: To be an effective contraceptive agent, the pill must be taken as directed. The synthetic hormones present in the pill inhibit ovulation by suppressing the secretion of the luteinizing hormone and the follicle stimulating hormone by the pituitary gland. Taking the pill irregularly fails to suppress these hormones.
Myth: If I ejaculate near the vagina but not inside, there is not danger of pregnancy.
Fact: There is some danger of pregnancy if ejaculation occurs outside but near the vagina. If enough moisture is present, the sperm can travel the short distance into the vagina and cause a pregnancy/stds.
Myth: The withdrawal method is fullproof.
Fact: The withdrawal method has probably caused more pregnancies than any other “birth control”. It simply does not work. Some of the penile lubricating fluid containing sperm can be deposited in the vagina long before withdrawal. In addition, ejaculation may occur in stages with the man being unaware that it has actually commenced; or he may not have the will-power to withdraw in time.
Myth: I can’t get pregnant the first time I have intercourse.
Fact: You certainly can. If your ovulating, you can get pregnant whether you have had sex before or not.
Myth: Douching is an effective method of birth control.
Fact: Douching is not an effective contraceptive method. Immediately after ejaculation, sperm enter the cervix out of reach of any douching solution ~ the douche may even speed the sperm on their way.
Myth: If a woman doesn’t have an orgasm, she won’t get pregnant.
Fact: It is not necessary to have orgasm at all in order to become pregnant.
Myth: I can’t get pregnant if we have intercourse standing up.
Fact: You certainly can. Positions during intercourse have nothing to do with contraception.