Observational study links late-pregnancy THC exposure with behavioral scores

OBJECTIVE: To identify critical windows of prenatal exposure to delta 9-tetrahydrocannabinol (Δ9-THC) and child neurodevelopment. STUDY DESIGN: We followed 460 mother-child pairs participating in the Healthy Start study through age 5 years. Δ9-THC and its metabolites were measured at about 17 weeks' gestation (n=460) and about 27 weeks' gestation (n=434) in maternal serum, and at birth via cord blood (n=238). At age 5 years, behavior was assessed via Child Behavior Checklist (CBCL) and cognition was assessed via NIH Toolbox. For each outcome, we fit a generalized estimating equation model with a Δ9-THC exposure variable, a timepoint variable, and an exposure-by-timepoint interaction term. RESULTS: Δ9-THC exposure prevalence was 8% at 17 weeks, 6% at 27 weeks, and 5% at delivery. Associations of Δ9-THC with most neurobehavioral outcomes were dependent on timing, with generally stronger signals for exposure at delivery. For instance, Δ9-THC exposure at delivery was associated with higher T-scores for attention problems (β=5.2, 95% CI: 2.3, 8.0), attention deficit hyperactivity disorder symptoms (β=2.4, 95% CI: 0.9, 3.8), and pervasive developmental problems (β=3.9; 95% CI: 0.8, 7.1), compared with children with no exposure at delivery. CONCLUSIONS: Δ9-THC exposure in late gestation showed particularly strong associations with adverse behavioral outcomes in early childhood. Our study suggests that it is never too late to quit cannabis use during pregnancy to limit adverse effects on child neurodevelopment.