Head circumference confounders

Neonatal Cocaine freely crosses the placental barrier, and prenatal exposure to cocaine alters neurobehavioral development in rat pups (Sobrian et al. 1990). The effects on humans exposed prenatally to cocaine is a complicated matter, because so many other concurrent factors contribute to development. Common confounds are prenatal care and maternal polydrug use. Prenatal cocaine use is associated with reduced gestational age, birth weight, body length, and head circumference (Richardson et al. 1999). In children exposed prenatally to cocaine, some studies have shown behavioral differences evident at 1 to 3 years of age (Richardson et al. 1993 Richardson 1998). Associations are also made with impulsivity and attention deficits at age 6 (Leech et al. 1999). 

The illustrative data are those for cord PbB as it relates to gestational age, birth weight, length, and head circumference. As shown in Table 3, the adjustment for Hct% attenuated the effect size for each measure in models without control of confounding variables. In models with covariate control, Hct% correction made little difference, probably because there was little variance that could be attenuated. In the absence of a definitive basis of choice for the perinatal period, these analyses are reported as empirical findings that may be related to the methodology employed in these studies. 

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