Answers to Frequently Asked Questions About...
Risk of Pregnancy
When can I take a pregnancy test and be sure that it is accurate?
If it has been at least 10 days since you had unprotected sex
and you have not gotten your period when you think you should have, you
can take a home pregnancy test to find out if you are pregnant. Before
that, a negative test result won’t be accurate, and you definitely
can’t tell if you’re going to get pregnant in the first
few days after sex – the time when you would be taking emergency
contraceptive pills (sometimes called "morning
after pills" or "day after pills"). If the test
is negative but you are still worried, you can take a second home
pregnancy test in another week. If the result is positive, you should
contact your health care provider to discuss your options, including
prenatal care or abortion.
If you think you might already be pregnant because your period is
late, you can take a home pregnancy test before using emergency
contraception – although it’s not necessary from a
medical standpoint. Emergency
contraceptive pills won’t work if you are already pregnant,
and they will not harm
you or your fetus.
Remember, emergency contraception
significantly reduces the chances
that you will become pregnant if you had sex and your birth control
failed, you didn’t use contraception, or you were
forced to have sex. You can take the morning
after pill for up to five days after sex, but they work better
the sooner they are taken after sex. A thorough and up-to-date academic
review of the medical and social science literature on emergency contraception
is available here 
.