I explain this by stating you are an ignorant dope, and you are spreading misinformation that may put people at risk. If that was not clear enough, here it is: Pregnancy does not result in an HIV positive test. If you knew how the tests work, you'd realize how stupid your comment is. Sounds to me like you are reading that crap from C Johnson et al.
False positves do occur among the general population( 0.2%), and multiple pregnancies among, hep b, drug abuse, blood tansfusions are among the factors that increase the chances of and EIA false positive, but the chances of the confirmatory WB also being positive are 1 in 100 000 (JAMA 2000)
HIV tests are at least 99.5% accurate this according CDC, Health Canada, Japan's NIH, British Health Services