Pregnancy tests measure the levels of HCG hormone (human chorionic gonadotropin), which can be detected as early as 7-10 days after conception. The HCG hormone is also called the pregnancy hormone and is created in the body when implantation in the uterus occurs. In most women this happens 6 days after conception but some studies show that in as many as 10% of women this implantation happens later than 6 days after conception.

Urine Pregnancy Tests
HCG is able to be detected by a home urine pregnancy test, or doctor administered urine test, with about 99% accuracy 10 days after conception. Urine tests are not foolproof, of course, but for most women they are very accurate - sometimes even before a missed period.

False negatives are more common than false positive results with a home pregnancy test, since only very rare medical conditions would mimic the presence of the HCG hormone. A woman could be pregnant without enough of the HCG hormone present in her urine to trigger the positive result on the pregnancy test, however, so if you have other symptoms of pregnancy you might choose to get a blood test to double check a negative home pregnancy result.

If you have a negative home pregnancy test result before your missed period, but have other symptoms of pregnancy, it could be a false negative. Try taking the test first thing in the morning when the HCG hormone is the most concentrated. Wait another week and then retest or schedule an appointment with a midwife or doctor.

Blood Tests for Pregnancy
Barring any lab error, a blood test by a health care professional is completely accurate and can determine a pregnancy within 7 days of conception. Your doctor or midwife will call you with the results in just a couple days. The blood tests will pick up the presence of HCG and so are considered much more sensitive than home tests.

If you get a negative pregnancy result, but your period doesn't begin and you feel that the negative result is incorrect, ask your doctor to recheck in case of a ectopic (or tubal) pregnancy. False positive results are usually only seen when a woman is taking medication with HCG in it.

Remember, most home tests are becoming more sensitive and can detect an early pregnancy right around the day of a missed period in many women. But in other women, especially those with longer cycles, it isn't uncommon for false negatives on the first testing.

Once you find out you are pregnant you have to decide how to tell your husband, partner, parents or other loved ones! Come to the pregnancy forums and tell us about how and when you told your family, or how you felt the first time you found out you were pregnant.

More Resources: The Pregnancy Book by Dr. Sears

Be sure to sign up for the free pregnancy newsletter!