Tolerable Life

To the Editor. Fetters and Tronick1 report finding diminished gross motor abilities at ages 4 and 7 months in children of cocaine-abusing mothers compared with controls. But by age 15 months no difference between the children of cocaine-abusing mothers and controls could be demonstrated. Because large numbers of children in both the cocaine-exposed and unexposed groups were found to be performing significantly less well than the normative samples on which the testing instruments in the study were based, the authors suggest that “programs targeted only at specific high-risk populations (eg, cocaine-exposed infants) may miss the even larger number of children that are at risk for motor problems.”I am skeptical of the findings of this study, and especially of its recommendations. Gross motor development in children has been well-studied. The finding that the gross motor performance of the control group was significantly behind that of the normative samples of the testing instruments suggests the possibility of either a problem with the norms of the testing instruments being used, or that the tests were being administered in a fashion that is significantly different from how the tests were originally standardized.Although there was a statistical difference between the gross motor performance of the cocaine-exposed and control groups at 4 and 7 months, I have doubts as to whether this can be attributed to cocaine exposure itself rather than some other associated factor. Furthermore, although there is a statistically significant difference between the two groups, I question its clinical significance in view of the equivalent gross motor scores at age 15 months.Children from both groups were enrolled in intervention programs. This is an uncontrolled variable that conceivably could have minimized any difference between exposed and control groups, particularly if more cocaine-exposed infants were enrolled in such programs than control infants.If studies of long-term drug effects on child development are going to be conducted, then the researchers must be willing to withhold intervention from these children to determine the natural progression of development. Without the use of a real control group, in which all variables except for drug exposure are controlled for, it will never be known with complete certainty whether cocaine use itself poses a significant risk to unborn children beyond catastrophic birth defects presumed to be caused by vasospasm, and whether any intervention provided to these children after they are born is truly effective.In Reply. Dr Cunningham's skepticism of the findings of our study is unwarranted. To suggest that a real control group should eliminate all variables except for drug exposure ignores the multiple risks to healthy development inherent in the lives of drug-exposed infants as well as infants raised in poverty. The interpretation of our data is based on the multivariate design and analysis of the study that reflects the realities of our subjects' lives. It is the analysis of the multiplicity of risks that is central to our study. Clinicians and researchers should strive to understand the complex interaction under which healthy development emerges and is promoted rather than continuing a search for the single, essential variable to explain developmental findings. From our data we suggest that the multiple risk factors associated with poverty have a detrimental effect on motor development without the addition of drug exposure.We chose the Peabody Scales of Motor Development rather than the Bayley because the norms on the Bayley were already in question as too many infants and toddlers were reaching the ceiling on this examination. The norms on the Peabody have not been questioned. To use the normed values from a standardized and norm referenced examination such as the Peabody, data must be collected as specified under the norming conditions. Our testers administered the Peabody examination according to the manual instructions and were highly reliable. The reason d'être of normed tests is to use them in exactly the manner we did, and our findings clearly indicate that all the infants in our study performed below the norm.Infants participating in an intervention program would be expected to improve gross motor abilities. If more exposed infants participated in these programs, they might be expected to “catch up” with their nonexposed peers. However, this did not occur in our study. Although more exposed infants did participate in intervention than controls (5 exposed, 1 nonexposed), the data show that performance of the exposed infants did not improve while the nonexposed infants declined at 15 months. The significant differences apparent earlier were no longer evident. The intervention may have prevented the cocaine-exposed infants from further decline but this would not explain the decline in performance of the nonexposed group. Furthermore, this decline, that Richmond called developmental attrition, occurred regardless of what one may think of a particular test or set of normative comparisons. We suggest that the decline in motor ability by the nonexposed group and the continuing poor performance of the exposed group is a result of multiple factors that put the children in our study in developmental jeopardy.