Beginning in 1967, studies raised concerns that LSD might produce genetic damage[19] or developmental abnormalities in fetuses. However, these initial reports were based on in vitro studies or were poorly controlled and have not been substantiated. In studies of chromosomal changes in human users and in monkeys, the balance of evidence suggests no increase in chromosomal damage. For example, white blood cells of people who had been given LSD in a clinical setting were examined for visible chromosomal abnormalities; overall, there appeared to be no lasting changes.[19] Several studies have been conducted using illicit LSD users and provide a less clear picture. Interpretation of this data is generally complicated by factors such as the unknown chemical composition of street LSD, concurrent use of other psychoactive drugs, and diseases such as hepatitis in the sampled populations. It seems possible that the small number of genetic abnormalities reported in users of street LSD is either coincidental or related to factors other than a toxic effect of pure LSD.[19] A 2008 medical review concluded, "The available data suggest that pure LSD does not cause chromosomal abnormalities, spontaneous abortions, or congenital malformations."[20] However, this refutation has not stopped this perennial legend from being told, nor has it stopped the jokes about such "mutations" allegedly messing up the children of the Baby Boomers.