One reason for a false positive pregnancy test may be what is called a chemical pregnancy. This means you may have had an early miscarriage which manifests itself as your period when the time comes. Some pregnancy tests are so sensitive that they can catch the earlier chemical composition of a pregnancy. This is why doctors often advise women to test for a pregnancy if they have definitely missed their period. Testing before you have missed a period may lead you to believe that you are pregnant only to have your hopes dashed when you get your period a few days after.
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When you are pregnant, your body begins to produce the hormone human chorionic gonadotropin (HCG). HCG is produced by the placenta during pregnancy, and is the hormone that a home pregnancy test detects. Your body begins to produce HCG about six days after an egg is fertilized and after the embryo implants in the uterus. Levels of HCG increase rapidly in a pregnant woman’s body and are detectable in urine. By the time you think you may be pregnant (usually after you miss your period), HCG levels are high enough that a home pregnancy test will detect them.
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