Dose-response effect of cocaine on newborn head circumference

Objective. To evaluate the relationship between head circumference, birth weight, and cocaine dose in healthy term and near-term newborns exposed to cocaine in utero. Methods. We used radioimmune assay (RIAH) of cocaine metabolite in maternal hair to quantify third trimester cocaine exposure in 240 healthy newborn infants (gestational age: >36 weeks). Cocaine exposure was categorized into 3 levels: no exposure (n = 136), low cocaine exposure (n = 52; RIAH: 2-66 ng/10 mg hair), and high cocaine exposure (n = 52; RIAH: 81-4457 ng/10 mg hair). We collected information on maternal demographic characteristics, the pregnancy, and the use of substances through a structured interview and from the medical record. Results. Means of birth weight, length, and head circumference of infants with high cocaine exposure differed significantly from those with low exposure and no exposure, but were similar between low exposure and no exposure. We used a multiple linear regression model to assess the association between newborn head circumference and cocaine level, adjusting for the effects of birth weight; gestational age; infant sex; and several maternal factors, including height, weight gain during pregnancy, syphilis during pregnancy, and the use of alcohol, cigarettes, marijuana, and opiates during pregnancy. Only birth weight, sex, and high cocaine exposure were significantly associated with newborn head circumference. The predicted head circumference deficit associated with high cocaine exposure (.44 cm) represents 34% of the unadjusted difference (1.28 cm) between mean head circumferences of infants in the high cocaine exposure and no exposure groups. Conclusion. Newborns exposed to a high level of cocaine in utero (RIAH: >81 ng/10 mg hair) exhibit asymmetric intrauterine growth retardation in which the head circumference is disproportionately smaller than would be predicted from the birth weight (head wasting). The deficit in head size associated with cocaine exposure may reflect the effects of a specific central nervous system insult that interferes with prenatal brain growth.