nerable to developmental toxins.7 Important data regarding dose-response curves and the relation of developmental outcomes to the severity of exposure in humans are essentially unavailable and, realistically, may be most adequately addressed through animal models. Research is needed to clarify how different drug-using patterns (amount, frequency, duration, method of drug taking) and the timing of drug exposure affect fetal development in order to refine models of teratogenesis for specific drugs of abuse.
As already noted, most illicit drug abusers also abuse nicotine and alcohol and frequently abuse more than one illicit drug. These drugs interact in the body, potentially causing additive, synergistic, or antagonistic effects. For example, studies have shown that the presence of cocaine and ethanol in the liver produces cocaethylene, a compound that is more cardiotoxic than cocaine and has a longer half-life (Hearn et al., 1991a,b). Additionally, the effects of opiate-cocaine interactions have not been studied beyond the newborn period. Studies of the consequences of maternal polydrug use on the developing fetus are needed to clarify areas and extent of drug interactions.
Objective quantification of dose exposure is problematic, particularly for drug exposure during the first trimester when pregnancy may not be recognized. Maternal self-reports of drug use can be inaccurate in the report both of actual use and of amount and frequency. One study found that 12 percent of marijuana use and 35 percent of cocaine use during pregnancy were not reported (Zuckerman et al., 1989c). One contributing factor to underreporting is fear of the legal consequences of disclosure (see Chapter 10). Continued efforts are required to develop drug abuse interviews that are appropriate for pregnant women.
Development of biological markers of exposure will assist in verification of self-reports of drug use. Advances in drug testing, of both fetal hair and meconium, can improve the detection of the presence or absence of drug exposure and may provide an approximation of cumulative dose
Areas of the brain develop at different rates. For example, dopamine receptors are more prevalent in certain areas of the brain early in development. Exposure to dopamine-related compounds, such as cocaine, may have a selective impact on these parts of the brain when exposure to the drug occurs early in pregnancy, while other parts of the brain that have not yet developed dopamine receptors may not be affected.