Q: What effects -- if any -- does marijuana use during pregnancy have on the fetus or child? Evidence-based answer: The effects are unclear. Marijuana use during pregnancy is associated with clinically unimportant lower birth weights (growth differences of approximately 100 g), but no differences in preterm births or congenital anomalies (strength of recommendation [SOR]: B, prospective and retrospective cohort studies with methodologic flaws). Similarly, prenatal marijuana use isn't associated with differences in neurodevelopmental outcomes (behavior problems, intellect, visual perception, language, or sustained attention and memory tasks) at birth, in the neonatal period, or in childhood through age 3 years. However, it may be associated with minimally lower verbal/quantitative IQ scores (1%) at age 6 years and increased impulsivity and hyperactivity (1%) at 10 years. Prenatal use isn't linked to increased substance use at age 14 years (SOR: B, conflicting long-term prospective and retrospective cohort studies with methodologic flaws)
