Impact of prenatal exposure to delta 9-tetrahydrocannabinol and cannabidiol on birth size and postnatal growth trajectories

Background: Prenatal exposure to cannabis (or more specifically, delta 9-tetrahydrocannabinol [Δ9-THC]) has been consistently linked to low birthweight. Animal models further show that Δ9-THC is associated with rapid postnatal growth. Whether this association is modified by breastfeeding is unknown.

Methods: In this exploratory study, we followed 128 mother-child pairs through 3 years. Urinary Δ9-THC and cannabidiol (CBD) were measured mid-gestation. Generalized linear models estimated the associations between Δ9-THC and neonatal body composition. A mixed-effects model estimated the association between Δ9-THC and body mass index (BMI) z-score trajectories. Interaction was assessed by a three-way product term (Δ9-THC × breastmilk months × age).

Results: Fifteen children (12%) had Δ9-THC exposure; three had concomitant CBD exposure. Prenatal exposure to Δ9-THC alone was associated with lower fat mass (-95 g, 95% confidence interval [CI]: -174, -14) and neonatal adiposity (-2.1%; 95% CI: -4.2, -0.4) followed by rapid postnatal growth (0.42 increase in BMI z-score per square root year; 95% CI: 0.12, 0.72). Breastfeeding modified this association (p = 0.04), such that growth was similar for those breastfed for 5 months whereas a shorter duration of breastfeeding was associated with 1.1 higher BMI z-score at 3 years (95% CI: 0.21, 2.05).

Conclusions: Our study suggests that prenatal exposure to Δ9-THC may alter early-life growth. Breastfeeding may stabilize rapid postnatal growth, but the impact of lactational exposure requires further investigation.