Prenatal Cocaine Exposure and Children’s Language Functioning at 6 and 9.5 Years: Moderating Effects of Child Age, Birthweight, and Gender

Whether prenatal cocaine exposure (PCE) is related to decrements in children's language during the elementary school years has not been established. Language is a critical component of school-aged children's successful academic and socio-emotional functioning (Rutter & Mawhood, 1991). Expressive language delays have been linked to poorer social competence (Horwitz et al., 2003) and, in some studies, behavior problems (Caulfield, Fischel, DeBaryshe, & Whitehurst, 1989). Most studies evaluating the relation between PCE and language have focused on toddlers and preschoolers, and results have been inconsistent. In several large covariate-controlled prospective studies (Hurt, Malmud, Betancourt, Brodsky, & Giannetta, 1997; Kilbride, Castor, Hoffman, & Fuger, 2000), no significant effects of PCE on language were found. Similarly, in prior research with the present cohort, no significant PCE effects were found on standardized measures of receptive or expressive language or on general measures of language maturity (utterance complexity, vocabulary types) derived from transcripts of spontaneous language at age 2 (Beeghly et al., 1996), or on verbal ability (verbal IQ) assessed with the Wechsler Preschool and Primary Scales of Intelligence (WPPSI-R) (Wechsler, 1989) at age 4 (Frank et al., 2005). In other large covariate-controlled prospective studies, significant PCE-related decrements in children's language functioning were reported, although specific findings vary. Singer et al. (2001) found that one-year-olds with heavier PCE had lower standard scores for auditory comprehension (receptive language) than unexposed infants, and lower total language scores than infants with either lighter PCE or no PCE. In a follow-up of this sample at age 4 (Lewis et al., 2004), PCE was related to poorer expressive and total language scores, but not receptive language scores, although children with PCE were more likely to have mild delays in receptive language. Morrow et al. (2003) found a significant effect of PCE (mediated by fetal growth) on children's aggregated total language standard scores at 4, 8, 12, 18, and 24 months using generalized estimating equations (GEE). In a later analysis of expressive and receptive language scores in the same sample at 36 months, heavier PCE was associated with lower expressive (but not receptive) language scores (Morrow et al., 2004). Although this finding remained significant after adjustment for children's fetal growth, prenatal exposure to other substances, gender, age at test, 3-year IQ, and maternal age, it was reduced to marginal significance (p = .06) after the caregiver's education and paternal involvement were added to the model, highlighting the importance of evaluating caregiving factors in behavioral teratology research with children. In smaller studies with heterogeneous samples and methods, conflicting results have been reported. In several studies, no significant PCE effects were found (Espy, Kaufmann, & Glisky, 1999; Hawley, Halle, Drasin, & Thomas, 1995; Phelps & Cottone, 1999) whereas in other studies significant PCE effects on standardized language scores (receptive, expressive, or both) were reported (Bender et al., 1995; Chapman, 2000; Johnson, Seikel, Madison, Foose, & Rinard, 1997; Nulman et al., 2001). However, prenatal exposure to other substances was not always controlled. Only a few prospective studies have evaluated the relation between PCE and language beyond the preschool period. Delaney-Black et al. (2000) found no significant effects of PCE on measures of six-year-olds' expressive language assessed using either standardized tests or language samples, in either bivariate or multivariate analyses. However, when vocabulary-based “low language” subgroups were created, children with PCE were more than twice as likely as unexposed children to be classified in the low language group. Prenatal nicotine exposure was also related to delayed language in this study. Bandstra et al. (2002) found a significant PCE effect on children's total language scores at 3, 5, and 7 years of age using longitudinal GEE analyses, controlling for relevant covariates. In a later analysis of these data, heavier PCE was also related to lower total language scores (Bandstra, Vogel, Morrow, Xue, & Anthony, 2004). Consistent with recent theoretical work emphasizing the importance of evaluating contextual factors in substance abuse research (Cicchetti & Luthar, 1999; Institute of Medicine, 1996; Neuspiel, 1995), most of the prospective studies reviewed above found that child gender and other risk and protective factors (e.g., birthweight, caregivers' education, verbal ability, home environment, and custody arrangements) were significantly related to children's language outcomes, regardless of their PCE status. Although less consistently evaluated, significant mediating or moderating effects have also been reported. In one prospective study, measures of fetal growth (e.g., birthweight) mediated the relation between PCE and total language scores in early childhood (Morrow et al., 2003) but not at later ages (3–7 years) (Bandstra et al., 2002). In both animal (Spear, Silveri, Katovic, Campbell, & Douglas, 2002) and human studies (Bennett, Bendersky, & Lewis, 2002; Delaney-Black et al., 2004), gender moderated PCE effects on developmental or behavioral outcomes. In other research, verbal scores were higher when children with PCE received case-managed versus routine-managed care, suggesting that environmental factors moderate PCE effects on children's verbal skills (Kilbride et al., 2000). Similarly, in prior studies with the present cohort, significant interactions of PCE with contextual factors (i.e., children's birthweight, custody arrangements, early intervention, birth mothers' parity, and public assistance) were observed for children's developmental and behavioral outcomes during early childhood (Beeghly, Frank, Rose-Jacobs, Cabral, & Tronick, 2003; Frank et al., 2002). To date, no published prospective cohort study has evaluated the relation of PCE to standardized measures of children's receptive, expressive, and total language skills beyond the age of seven, when academic demands on language comprehension and production increase. This research is needed because PCE is hypothesized to affect areas of the brain associated with complex neurodevelopmental processes including language that cannot be reliably measured until school-age (Frank, Augustyn, Knight, Pell, & Zuckerman, 2001; Mayes, 1999). The aim of the present analysis was to evaluate whether PCE, or the interaction between PCE and child age, gender, or other contextual variables, was independently associated with children's receptive or expressive language at 6 and 9.5 years of age, after controlling for relevant covariates. Based on a cumulative risk perspective (Sameroff, Seifer, Baldwin, & Baldwin, 1993), the researchers expected that contextual risk factors (e.g., lower birthweight) would mediate or moderate any PCE effects on language found, such that exposed children with other elevated risks would have lower language scores.