How Pregnancy Tests Work

Pregnancy tests look for a special hormone, called human chorionic gonadotropin (hCG) that is only present in a woman’s blood or urine when she is pregnant. After successfully implanting into the lining of the uterus, this hormone is produced by the placenta of the developing embryo. Typically this occurs six to 10 days after conception. Levels of hCG increase rapidly, doubling every one to two days for approximately 10-12 weeks, then reducing to a stable level throughout the rest of the pregnancy. This hormone stimulates the ovary to continue secreting high levels of estrogen and progesterone needed to maintain the pregnancy.

HCG can be detected by carrying out either urine or blood tests. Blood tests must be arranged by your doctor and can pick up pregnancy as early as seven to 12 days after conception. As well as confirming whether hCG is present, blood tests can also show the exact levels of the pregnancy hormone.

Urine tests can be carried out by your doctor or in the privacy of your own home using a home pregnancy test (HPT). If a home pregnancy test is positive, it is recommended that you see your doctor immediately so that your results can be affirmed, helping to keep both you and your baby healthy.

There are a number of home pregnancy tests available on the market. Most are 99% accurate but only if the hCG levels are high enough to be detected. Some brands of tests are capable of detecting hCG at very low levels and are therefore able to be used seven to 10 days after conception. Because timing of ovulation and implantation and hCG levels can vary from woman to woman if testing early, it is possible to get a negative result and still be pregnant. Therefore most brands of home pregnancy tests recommend that if you do not get your period within seven days you should retest again. If this too is negative and your period does not return, you should contact your doctor.

Home pregnancy tests are available in test strips, cards and midstream styles and all come with detailed testing instructions.

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