BACKGROUND: Cannabis is the most frequently used illicit drug among pregnant women, but data describing the effects of prenatal cannabis exposure and concurrent nicotine and cannabis exposures on neonatal growth are inconsistent. Testing of meconium, the first neonatal feces, offers objective evidence of prenatal cannabis exposure, but the relative ability of meconium testing and maternal self-report to identify affected neonates remains unclear. METHODS: Eighty-six pregnant women provided detailed self-reports of daily cannabis and tobacco consumption throughout pregnancy. Cannabinoids and tobacco biomarkers were identified in oral fluid samples collected each trimester and quantified in meconium at birth. RESULTS: Cannabis-using women were significantly more likely to...