Short answer
No amount of cannabis is known to be safe during pregnancy. The CDC, the American College of Obstetricians and Gynecologists (ACOG), the FDA, and the National Institute on Drug Abuse (NIDA) all advise against cannabis use while pregnant or breastfeeding. THC crosses the placenta and reaches fetal tissue. State legality does not change the clinical guidance.
Cannabis and Pregnancy: A Cost of Care Buying Guide
What the major health agencies say
- CDC: advises against cannabis use during pregnancy and while breastfeeding. Federal survey data place past-month cannabis use near 7 percent of pregnant women, and near 15 percent of pregnant women aged 18 to 24.
- ACOG: states that no amount of marijuana has been proven safe in pregnancy, and recommends screening and counseling at the first prenatal visit.
- FDA: has not approved any cannabis or CBD product for use in pregnancy.
- NIDA: reports that THC may disrupt fetal brain development, since the fetal brain has cannabinoid receptors from early gestation.
How THC reaches the fetus
THC is fat soluble. It moves across the placenta and into cord blood. Published studies report fetal THC concentrations in the range of 10 to 30 percent of maternal blood levels. THC and its metabolites also concentrate in fat tissue, so clearance takes days. A single use can produce detectable levels in urine for several days, and in heavy users for weeks.
Outcomes linked to prenatal cannabis use
Most data come from observational studies of self-reported use. Studies report higher rates of:
- Low birth weight and small-for-gestational-age infants
- Preterm birth before 37 weeks
- Stillbirth
- Admission to the neonatal intensive care unit
- Lower Apgar scores at 1 and 5 minutes
Longer-term studies track attention, memory, and impulse control in children exposed before birth. Results are mixed. Many studies cannot separate cannabis from tobacco, alcohol, and socioeconomic factors, which limits what the data can prove.
what does cannabis do to a fetus
Breastfeeding
THC passes into breast milk. It is detectable in milk for days after the last use. CDC and the American Academy of Pediatrics advise against cannabis use while breastfeeding. Infant effects reported in small studies include sedation and slower motor development. No safe threshold has been established.
What is not known
No randomized controlled trial has tested cannabis in pregnancy. Dose, route, potency, and timing of exposure vary across studies. Research on CBD in pregnancy is thin. Evidence on edibles compared with inhaled cannabis is also limited.
What to do
- Tell your clinician about any cannabis use, including CBD, before or at the first prenatal visit.
- Ask about treated options for nausea and vomiting, such as doxylamine and pyridoxine, or other antiemetics.
- Do not stop a prescribed medication on your own.
- Ask about counseling or a quit line if stopping is hard.
Some clinics test urine for THC at the first prenatal visit. Laws on reporting a positive test to child welfare agencies differ by state. Ask your clinician what your state requires.