by toxicological analysis, and subjects may not reveal their true drug use, especially in the case of illegal drugs. Thus, there can be undetected drug users in the comparison group and information on use of other drugs or quantity and frequency of drug use may be suspect. Few of the above studies examined dose response relationships between drug use during pregnancy and imaging results, although the two studies of dose response relationships between prenatal cocaine exposure and neuroimaging were longitudinal studies that included toxicological verification32, 34.
