A review found that despite study limitations, accumulating data links prenatal marijuana exposure to decreased birth weight, spontaneous preterm birth, and impaired neurodevelopment, with THC also detected in breast milk.
Read this if you're pregnant or planning pregnancy and want to understand the evidence on marijuana risks during pregnancy.
Professional societies recommend against marijuana use during pregnancy and breastfeeding
What the researchers found
Marijuana is the most commonly used illicit drug during pregnancy, and its use is increasing in the US. While much of the existing research has limitations (study design, confounding factors), a growing body of data suggests adverse outcomes from prenatal exposure.
Associations have been identified with decreased birth weight, increased spontaneous preterm birth, and impaired neurodevelopment among children and adults who were exposed in utero. Moderate concentrations of marijuana have also been detected in breast milk.
Multiple professional societies have issued clear statements against marijuana use during pregnancy and lactation.
Why it matters
As marijuana becomes more available and socially accepted, pregnant women may perceive less risk from use. This review highlights that despite imperfect evidence, the signal for harm is consistent enough that professional medical organizations recommend against use during pregnancy and breastfeeding.
The numbers in context
Marijuana: most commonly used illicit drug in pregnancy. Prevalence increasing in US. Associations: decreased birth weight, increased preterm birth, impaired neurodevelopment. THC detected in breast milk at moderate concentrations.
How the study worked
Narrative review of existing research on marijuana use during pregnancy, covering birth outcomes, neurodevelopmental effects, and breast milk transmission.
What this study cannot tell us
Existing research is limited by observational designs, confounding factors (tobacco, alcohol, socioeconomic status), and self-reported cannabis use. THC potency has increased substantially over time, so older studies may underestimate current risks. The review does not differentiate between occasional and heavy use.
How to read the evidence
Narrative review of observational studies. Consistent signal for harm but limited by study design and confounding in the underlying evidence.
When this study was published
Published in 2017. Research on prenatal cannabis exposure has continued with more attention to product potency and delivery methods.
The bigger picture
The challenge with prenatal cannabis research is that randomized trials would be unethical, so all evidence is observational and subject to confounding (women who use marijuana during pregnancy may also smoke tobacco, use alcohol, have poorer nutrition, etc.). Despite these limitations, the consistency of findings across studies has been sufficient for professional societies to advise against use.
Questions still open
- Does the route of cannabis administration (smoking vs edibles) affect prenatal risk? At what trimester is exposure most harmful? Would CBD without THC carry the same risks?
Common questions
Is marijuana safe during pregnancy?
Does marijuana get into breast milk?
Read the original research
Marijuana Use in Pregnancy: Concerns in an Evolving Era.
Journal of midwifery & women's health, 62(3), 363-367
Citation
Foeller, Megan E; Lyell, Deirdre J. (2017). Marijuana Use in Pregnancy: Concerns in an Evolving Era.. Journal of midwifery & women's health, 62(3), 363-367. https://doi.org/10.1111/jmwh.12631
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