Cognitive and Motor Outcomes of Cocaine-Exposed Infants

Abstract

Since the crack cocaine epidemic began in the mid-1980s, an estimated one million children have been born after fetal exposure. Although cocaine is known to affect monoaminergic neurotransmitter systems important to the developmental of neuronal circuits and human learning, few longitudinal studies of cocaine-exposed infants have been carried out. Because maternal cocaine use still is a substantial problem, especially in urban areas of the United States and in women of low socioeconomic status, a prospective birth cohort study was carried out in 415 consecutive infants primarily from a high-risk population. A history of cocaine exposure was obtained for 218 infants. A majority of both groups were black, had low incomes, were unemployed, and had no more than a high school education. Follow-up was 94% up to age 2 years. The Bailey Scales of Infant Development were administered at ages 6.5, 12, and 24 moths. They include the Mental Development Index (MDI), which reflects memory, language, and problem-solving ability, and the Psychomotor Development Index (PDI), which estimates motor control and coordination. Half the participants received the Home Observation for Measurement of the Environment (HOME) test at 2 years. Women using cocaine reported using alcohol, tobacco, and marijuana more often than cocaine nonusers. The exposed infants weighed less at birth, had lower gestational ages, had smaller head circumference than unexposed infants, and were shorter. More exposed infants were cared for by persons other than the mother at both 1 and 2 years of follow-up. Cocaine-exposed children did less well than their unexposed peers on the Bayley tests after adjusting for significant confounding variables. The average MDI dropped in both groups over time but substantially more in children exposed to cocaine. The differences persisted after controlling for race, gender, and HOME score at age 2 years. Using a MDI below 70 at age 2 years as a measure of mental retardation, 13.7% of exposed children and 7.1% of those not exposed were so classified. Mild developmental delay also was more prevalent in the exposed group. Cocaine did not significantly influence psychomotor development; PDI scores rose significantly in both groups of children during follow-up. Children in this study who were exposed to cocaine in fetal life were twice as likely as nonexposed children to exhibit significant cognitive deficits during the first 2 years of life. This finding adds to the urgency of promoting public health initiatives to prevent substance abuse.