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).
The Maternal Health Practices and Child Development study (MHPCD) of 564 high-risk pregnancies in predominantly minority women of low socioeconomic status followed infants from birth through 14 years of age.1,3-5,7,8 It found some small differences in outcomes among children exposed to marijuana prenatally. Of note, when investigators evaluated marijuana use at age 14 years, they compared adolescent self-report history with urine THC testing (specificity 78%).
The MHPCD study was limited because, compared with the nonusing group, mothers who used marijuana were also 20% to 25% more likely to be single and poor, to live in poorer quality homes, and to use alcohol, tobacco, and other drugs. Investigators used statistical modeling to account for these environmental differences and estimated that 10% of the difference in outcomes was attributable to prenatal marijuana exposure.
The Generation R study (Gen R) enrolled 220 lower-risk pregnancies in multiethnic European women of higher socioeconomic status, followed children to 3 years of age, and found no marijuana-associated differences in any parameter.1,3,4 The final assessment included only 51 children.
RECOMMENDATIONS
The American College of Obstetricians and Gynecologists (ACOG) recommends screening all women for tobacco, alcohol, and drug use (including marijuana) during early pregnancy.9 Women who report marijuana use should be counseled regarding potential adverse consequences to fetal health and be encouraged to discontinue use.
ACOG says that insufficient data exist to evaluate the effects of marijuana use on infants during lactation and breastfeeding and recommends against it.
The American Society of Addiction Medicine also recommends screening pregnant women for drug use and making appropriate referrals for substance use treatment.10
