Significant Deficits In Mental Skills Observed In Toddlers Exposed To Cocaine Before Birth

The study, which was funded by the National Institute on Drug Abuse (NIDA), is published in the April 17, 2002 issue of the Journal of the American Medical Association.

Dr. Glen R. Hanson, Acting NIDA Director, said, "This study adds important new evidence to a growing body of knowledge. It is the first report of a clear-cut relationship between prenatal cocaine and mental test performance at age two. These findings remind us of the importance of continued efforts to determine which children and families are at risk because of exposure to cocaine, so we can prevent or ameliorate negative consequences of using this drug." He added, "It is important that in this research process, we avoid inadvertently labeling or stigmatizing large numbers of toddlers because of drug use by their mothers during pregnancy. We want to use this type of research to help us be more effective in how we work with these children."

The investigators followed the developmental course of 415 infants, whose pregnant mothers were recruited into the study at a large urban county teaching hospital between the years 1994 and 1996. All of the pregnant women recruited into the study were from high-risk and low-socioeconomic status backgrounds. Urine samples were collected from the women and meconium samples were collected from each baby. These samples were screened for maternal drug use. Two hundred and eighteen infants were found to be cocaine-exposed and 197 to be cocaine-free.

Each infant was tested for developmental progress at 6.5, 12, and 24 months of age. The infants were administered the Bayley Scales of Infant Mental and Motor Development, a widely used assessment of infant development. Scores on this assessment measure memory, language, and problem-solving abilities, as well as gross and fine motor control and coordination.

While no effects on the Bayley Motor Scale were detected, the cocaine-exposed children performed more poorly on the Bayley Mental Scale than unexposed children, after adjusting for other variables (such as use of alcohol, tobacco, or other drugs; maternal age; prenatal care, and home environment quality). Although mental development index scores decreased over time for both groups of infants, children prenatally exposed to cocaine had scores that decreased faster. From 6.5 to 24 months, the average score for infants exposed to cocaine declined by 14 points compared to 9 points for unexposed children.

Almost 14 percent of the cocaine-exposed infants had scores in the mental retardation range, 4.89 times higher than expected in the general population. The percentage of children with mild or greater delays was 38 percent, almost double the rate of the non-cocaine-exposed group. Infants of mothers with evidence of higher and more frequent cocaine use during pregnancy fared the worst.

Lead investigator Dr. Lynn T. Singer said that there are several possible mechanisms by which cocaine exposure during pregnancy may affect infant outcome. Developing neural systems of the fetal brain may be directly and adversely affected by cocaine exposure. Another possible explanation is that cocaine use during pregnancy may constrict the vascular system, subsequently decreasing blood flow through the placenta and resulting in low oxygen levels (hypoxemia) in the fetus.

Differences in the cocaine-exposed infants were noted at birth. These infants had lower gestational age, lower birth weight, and smaller head circumference and length than unexposed babies. There were more preterm, low birth weight and small-for-gestational age infants in the exposed group. There were 11 deaths by the time the infants were 2 years old, 8 in cocaine-positive children and 3 in cocaine-negative children. Sudden Infant Death Syndrome (SIDS) was the leading cause of death in both groups.

An estimated 1 million children have been born after fetal cocaine exposure since the mid-1980's, when the so-called crack epidemic emerged with the availability of a cheap, potent, smokable form of cocaine.