False positive results appear quite rarely, though they are possible, as there are some instances and conditions, when they can occur. In case if you obtained a false positive result from the pregnancy test, performed at home conditions, it is usually the result of faulty test strips. That is why nowadays most home pregnancy tests are equipped with a special indicator, which lets a woman see whether or not the test working correctly. In addition, there are some certain health conditions, when a home pregnancy test may show false positive result, like if a non – pregnant woman has some tissues, which can produce HCG, though these HCG levels are so extremely low, that they are usually not detectable by home pregnancy tests. The false positive result may also occur, if the conception has not developed into pregnancy, which does occur with half of them. The so – called “chemical pregnancy” (a pregnancy, in which there are no other signs of symptoms, except the positive pregnancy test’s results) takes place in these cases However, if a woman leaves her performed pregnancy test too long before checking it, this can also cause a false positive result of the test, because as the time goes by, the urine will soak through the test, exposing the chemical strip, indicating pregnancy.

Urine pregnancy tests, performed at home, as well as blood pregnancy tests, performed at the doctor’s office, may give false positive result if a woman is taking some kind of HCG containing fertility drugs.

It is also possible to obtain a false negative result (it means that the test will say you are not pregnant, and you really are), especially if a pregnancy test was performed too early in pregnancy. Actually, false negative results are more common than false positive ones. During first days of pregnancy women normally do not have high levels of HCG, and the amount a woman has may not be sufficient to detect for either a urine or blood test with not very high sensitivity.

One more reason of the possibility of a false negative result is the point that every woman ovulates at different times in her menstrual cycle; moreover, embryos also get implanted into the uterus at different times. That is why the accuracy of home pregnancy test results varies from woman to woman.
Anyway, no matter what result you obtained, it would be better to repeat your pregnancy test in about a week or so.

Can Anything Interfere With the Pregnancy Tests Results?
Most medicines, which are available over – the – counter, as well as those, which need doctor’s prescription to be obtained, including birth control pills and antibiotics, should not interfere with the results of a performed pregnancy test (no matter whether it is blood clinical pregnancy test or urine home pregnancy test). However, the only medications, which can cause a false positive result (it means that the test shows a woman is pregnant, when she is really not) of a pregnancy test are those, containing HCG. These HCG containing medicines are applied sometimes while treating infertility. That is why you should better consult your doctor taking into consideration appropriate times and circumstances for performing pregnancy tests.
Alcohol and drugs do not influence the pregnancy test result; however, if a woman thinks that she might be expecting a baby, she should not use any of the abovementioned substances.