Cannabis use has increased rapidly in recent years, with everyone from famous pop stars to wholesome grandmas gushing about the plant’s medicinal properties. Many questions have arisen as a result, but perhaps one of the most extensive debate centers on the use of cannabis during pregnancy.
Studies suggest that we should worry about the potential risks for pregnant women who consume cannabis. However, these studies are small in number and inconclusive.
Figuring out exactly how cannabis affects a growing fetus is more challenging than it may seem. Historically, researchers have been limited by cannabis illegality. Running a cannabis study requires forging through mounds of red tape and restrictions.
Most studies on cannabis and pregnancy choose individuals who smoke or vape. But what about consuming cannabis-infused food and drinks? Or using a tincture or oil? It’s possible that one cannabis consumption method could harm a fetus while the others are harmless.
Timing is tricky too. Smoking a joint during the first trimester likely carries different implications than sparking up just before the baby is due.
Considering these challenges, it’s easy to understand why there are still uncertainty regarding the effects of cannabis during pregnancy. There have been a few risks tentatively identified, however.
Risk #1 — Impaired Cognition
Much of the research we have on cannabis and pregnancy focuses on cognitive development. Multiple studies have found that children exposed to cannabis in the womb exhibited intellectual deficits later in life. These children demonstrated poorer memory, attention spans, and problem-solving skills.
A 2008 study concluded that heavy cannabis use affected verbal reasoning in the first trimester, short-term memory and quantitative reasoning in the second and third trimesters. 
However, according to a systemic 2020 review, the “totality of the evidence suggests prenatal cannabis exposure does not lead to cognitive impairments.” 
So, what’s going on? It may be that there are confounding factors at play. For instance, if women who use cannabis during pregnancy are more likely to be ill because coming from poorer surroundings, that could affect their children’s cognitive ability. Studies with a small sample size might confuse cannabis for environmental factors.
Risk #2 — Low Birth Weight
Low birth weight is another possible outcome of cannabis use while pregnant. Many studies have found that pregnant women who used cannabis were more likely to have a baby with a lower birth weight.
This matters because low birth weight can lead to health problems like respiratory infection, heart disease, and diabetes later in life. Low birth weight babies also tend to need longer hospital stays.
Once again, however, the research is inconclusive. The American College of Obstetricians and Gynecologists asserts that women who use cannabis less than once a week are not at an increased risk for an underweight birth.
Risk # 3 — Smaller Head Circumference
Numerous studies have explored the effects of cannabis use on head circumference, an important predictor of neurological development. Some concluded that babies born to women who used cannabis during pregnancy were smaller in head size than those born to women who abstained from the substance.
It’s unclear why this might be the case, but a few theories exist. It could be that cannabis disrupts the development of certain parts of the brain, leading to slower growth. Or perhaps it’s because cannabis use can increase nausea and vomiting during pregnancy, inhibiting the baby’s proper nourishment.
As you can see, there’s still much debate surrounding the safety of using cannabis while pregnant. It seems clear that more research is needed to draw any definitive conclusions.
That said, if you’re pregnant or trying to become pregnant, speak to your doctor. It may be advisable to avoid cannabis completely until more studies have been conducted.
- Goldschmidt, Lidush et al. “Prenatal marijuana exposure and intelligence test performance at age 6.” Journal of the American Academy of Child and Adolescent Psychiatry vol. 47,3 (2008): 254-263. doi:10.1097/CHI.0b013e318160b3f0
Torres, Ciara, et al. “Totality of the Evidence Suggests Prenatal Cannabis Exposure Does Not Lead to Cognitive Impairments: A Systematic and Critical Review.” Frontiers in Psychology, vol. 11, 2020, American College of Obstetricians and Gynecologists