Marijuana And Pregnancy #3: What Happens Inside The Womb

Can marijuana impact your baby’s development inside the womb? Here’s a glimpse into the ongoing debate on marijuana and pregnancy series.

Mar 28, 2016

Over the past couple of weeks, we’ve looked at the pros and cons of breastfeeding while using marijuana, as well as the herb’s potential impact on those struggling with fertility. In this piece, we’ll look at what happens to the fetus inside the womb when you use marijuana during pregnancy.

Marijuana and pregnancy

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If you’re having fertility issues, marijuana may not make conception any easier. But, once you become pregnant, the effects of the plant are much more mysterious. In an interview with Vice,  Dr. Dimitrios Mastrogiannis of the University of Illinois in Chicago claims that there is little data linking marijuana use to adverse neonatal outcomes.

Yet, because little research has been done, Dr. Mastrogiannis qualified that we can’t say for sure that there are no negative effects. Just as the scientific verdict is split when it comes to marijuana use while breastfeeding, research is split when it comes to marijuana’s impact on babies inside the womb.

What we do know for sure is that there are a lot of women out there who have consumed marijuana throughout pregnancy.  In fact, cannabis is the most common illicit substance used by pregnant women in Western societies. Many of those women now have healthy, talented, and thriving children.

Marijuana also has a long history of being used as a labor aid and anti-nausea medication in various ancient cultures around the world. In Tibet, for example, hemp preparations were commonly given to women to ease labor pains and combat post-partum depression. Of course, today’s cannabis is super-charged with THC while what our ancestors had likely was not.


One of the huge downfalls of the political climate surrounding cannabis research is that the majority of studies focus on psychoactive THC. With CBD strains and products becoming more readily available, many soon-to-be mothers want to know if sticking to other cannabinoids reduces any pregnancy risks. Unfortunately, the effects of other cannabinoids are mostly yet to be determined.

The ECS inside the womb

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The endocannabinoid system (ECS) is key to creating the perfect environment for an embryo and a fetus. The endocannabinoid system is a large, regulatory network of cell receptors and corresponding compounds in the body. It’s responsible for maintaining bodily homeostasis, meaning it facilitates the optimum, balanced environment for overall health. Cannabinoid receptors are found all throughout the body, including inside the womb.

Over the past decade, the ECS has been found to play a major role in female reproduction. Research has found that the ESC aids in:

  • Blastocyst formation. A blastocyst is an early collection of cells that eventually form an embryo.
  • Transport of an egg through the fallopian tube.
  • Implantation of the embryo in the uterus.
  • Pregnancy maintenance.
  • The transformation of the endometrium (the lining of the uterus) into the decidua. This is where an embryo implants during a pregnancy.
  •  The development of the placenta.

The ECS is also crucial to fetal brain development.  Thus far, the scientific community doesn’t know a whole lot about the exact ways endocannabinoid signaling assists in neurodevelopment. But, recent research has found that it aids in central nervous system patterning. Namely, the ECS lends to the creation of mood, cognition, and reward centers of the brain in fetuses. This makes a lot of sense, as these are the same parts of the brain that the ECS impacts in adults.

Marijuana and the developing brain

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Marijuana’s influence on the developing brain is probably the biggest concern for medical professionals and parents alike. Both in the womb and shortly after birth, an infant’s brain is undergoing an intense period of development. When doctors and researchers express concern about marijuana-exposed babies, it’s in part because of the critical role the endocannabinoid system plays in the development process.

Can the placenta protect your baby?

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According to the American Acadamy of Pediatrics, the placenta may block the mother’s THC metabolites from reaching the fetus. Though, THC itself can pass through. None the less, the placenta does seem to decrease THC exposure. Early animal research has found that concentrations of the cannabinoid are much lower inside of the placenta than those in the mother. This is slightly unusual since the placenta does not protect the baby from harms from many other drugs. Yet, the more you smoke, the more likely it is for the fetus to be exposed to THC.

Using rodent models, researchers have estimated that one-third of the THC in a mother’s blood plasma can cross the placenta barrier. Because some THC crosses the placenta, it can enter the fetal bloodstream and cross into the developing brain.

The brain conundrum

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If you do a search for available information, you may quickly find that a lot of the research on marijuana’s impact inside the womb is pretty split. Though there is evidence that THC can cross into the fetal bloodstream, whether or not this has lasting impacts is unclear. On one hand, some scientific studies have suggested that prenatal marijuana use may alter a child’s behavior in the long run. Yet, on the other, centuries of historical use and a wealth anecdotal testimonies from marijuana-consuming mothers have a very different tale to tell.

To start with the bad news, one study published in 2000 that suggested exposed infants were prone to hyperactivity, impulsivity, and inattention by the age of 10. These negative effects were correlated to women who smoked at least one joint every day during the first and third trimesters of pregnancy.

A more recent study published in the EBMO Journal in 2014 tested the effects of THC in human tissue and in animal models. The researchers trying to find out whether or not THC had an impact on brain development while children were still in the womb. They found that the cannabinoid changes the way nerve cells build connections and communicate with each other. This happens most profoundly in the cerebral cortex, the part of the brain responsible for memory, cognition, and language. To put these findings in context, Dr. Tibor Harkany of the Karolinska Institutet explained:

Even if THC only would cause small changes its effect may well be sufficient to sensitize the brain to later stressors or diseases to provoke neuropsychiatric illnesses in those affected in the future.

But, not so fast…

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Hardly any studies have followed those prenatally exposed to marijuana into adulthood. This makes it difficult to evaluate the strength of the claims made by research like that listed above. Even if marijuana changes some of the neural connections in the brain, does this lower a person’s quality of life or cause significant harm in the long run? Many mothers and exposed children themselves argue that this is not the case.

A longitudinal study conducted in Jamaica by Dr. Melanie Dreher in the 1980s put behavioral and cognitive implications to the test. The researchers followed 24 children of marijuana-consuming mothers for 5 years post-pregnancy. Dr. Dreher and her team found absolutely no difference in the cognitive, motor, and behavioral skills between babies exposed to marijuana in the womb and non-exposed controls. In fact, the children who were exposed to cannabis prenatally actually performed better on several tests 3 months after birth.

But, what happened when Dr. Dreher and her team examined the children again when they were 5-years-old?

They found absolutely no differences between exposed and non-exposed children. What they found instead were significant differences in children who regularly attended school and those who did not. Those who went to school tended to perform better on cognitive and behavioral tests than children who lacked the opportunity. No surprise, really.

Unfortunately, Dr. Dreher and her team did not have the funding to continue to follow the children into adolescence.

THC metabolism by the fetus

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The major mystery here is how developing organisms, like infants, breakdown and use THC once it enters the bloodstream. A 1987 study published in Toxicology and Applied Pharmacology tested for the presence of THC and THC metabolites in rhesus late-term monkey fetuses. The mother monkeys had been given a dose of THC, and the researchers compared how much of the compound entered the fetus versus the mother.

While THC was present in the tissue of various fetal organs, hardly any metabolites were found. The mothers converted THC into its most common metabolite, 11-nor-hydroxy-THC, within about an hour. Mother blood levels of the cannabinoid were 44 nanograms per milliliter, while levels in the fetus were under five nanograms.

Metabolizing THC is the process the body goes through to break down and experience the high that marijuana is known for. The fact that THC was not metabolized by the fetus hints that the developing money did not process the psychoactive in the same way as the adult.

Though human infants can test positive in urine tests after birth, this observation is supported by a theory presented by Israeli researcher Ester Fride. In a 2004 review, she writes:

…prenatal exposure to the active constituent of marihuana (Δ9-tetrahydrocannabinol) or to anandamide affects prefrontal cortical functions, memory and motor and addictive behaviors, suggesting a role for the endocannabinoid CB1 receptor system in the brain structures which control these functions. Further observations suggest that children may be less prone to psychoactive side effects of Δ9-tetrahydrocannabinol or endocannabinoids than adults. The medical implications of these novel developments are far reaching and suggest a promising future for cannabinoids in pediatric medicine for conditions including “non-organic failure-to-thrive” and cystic fibrosis.

While Fride’s findings agree that THC exposure can cause brain changes, she articulates that children may experience weaker psychoactive side effects, should this hypothesis hold true in humans. Developing bodies put the compound to use in a different way than adult bodies do. What do developing bodies do with the cannabinoid, exactly? What does this mean for overall development? At this point, it’s difficult to say.

What the AAP has to say

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Regularly consuming any substance while pregnant (be it marijuana, coffee, or even a particular food) has an effect on a developing fetus. Unlike nicotine or alcohol, the American Academy of Pediatrics (AAP) has found that prenatal cannabis use has not been associated with strong detrimental effects after birth. A 2013 review comparing the prenatal implications of various drugs found that marijuana does have some impacts on things like behavior and cognition, but the effects were not as strong as other substances. Here’s a summary of the short and long term effects highlighted by the AAP:

Prenatal marijuana use has no effect on:

  • Fetal growth
  • Long term growth
  • Fetal abnormalities
  • Post-birth substance withdrawal
  • Long term language abilities

Prenatal marijuana use has an effect on:

  • Neurobehavior
  • Long-term behavior
  • Long-term achievement
  • Long-term cognition

The review compared literature on nicotine, alcohol, marijuana, opiates, cocaine, and methamphetamines. Of the six drugs examined, marijuana was the least harmful. Though, there was a lack of sufficient evidence regarding prenatal methamphetamine use.

The most harmful as alcohol, which correlated with strong negative effects on everything but neurobehavior, language, and withdrawal symptoms. Alcohol had negative effects on neurobehavior and language, they just weren’t strongly negative. Booze-exposed babies did not show withdrawal symptoms post-birth. There is more information on prenatal alcohol and tobacco use than on prenatal cannabis consumption.

Some contentions

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The one point of contention with this report is that it does not incorporate studies which have shown no difference between healthy controls and marijuana-exposed infants. For example, the article cited a study that found that exposed newborns are prone to tremors and startling. Yet, a study by Katherine Tennes from 1982 tested newborns for the same symptoms and found no correlation between marijuana exposure and increased tremors or startles.

Findings from Dr. Dreher’s and Dr. Fride’s studies were not included in the AAP review. Neither was a 1989 study that found that there were few behavioral effects associated with moderate prenatal marijuana use.

What is it all worth?

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When you purchase recreational cannabis in the state of Oregon, you’ll get a little slip of paper warning you that the herb might harm your baby. While the precise risks have yet to be weighed completely by the scientific community, governments and medical providers are taking precautions.

But, there are certainly people out there who have been exposed to cannabis in the womb and now lead very happy, successful, and fulfilling lives. It’s not uncommon to hear a proud marijuana-consuming mother mention that her child is now in an accelerated learning program. Many mothers out there swear that marijuana, be it in the form of a tea, edible or dried bud, was a saving grace during their pregnancy.

At a conference on medical marijuana, Dr. Dreher of the Jamaican study mentioned above explains:

We can’t really conclude that there’s necessarily no impact from ganja use prenatally whatsoever, but what can be concluded is that the child who attends basic school regularly, is provided with a variety of stimulating experiences at home, who is encouraged to show mature behavior, has a profoundly better chance of performing at a higher level on the skills measured by the McCarthy whether or not his or her mother consumed ganja during pregnancy.

The McCarthy scale is a standard form of measurement for testing children’s cognitive abilities. The results of Dreher’s anthropological study indicate that a healthy home and learning environment are incredibly important factors for cognitive and behavioral progress in children. Access to these safe and engaging spaces was a much better indicator of success than was prenatal marijuana use.

While research suggests that THC may affect fetal brain development in the womb, it’s very difficult to determine the extent of the harms. Evidence from Dr. Dreher’s study, as well as anecdotal evidence, attests that marijuana-exposed children can be just as healthy and cognitively engaged as non-exposed children. That is, as long as the children are given the resources they need to excel. Yet, at the same time, many medical professionals and parents argue that anything that potentially influences the way an infant’s brain develops should be avoided.

If personal accounts are worth anything, marijuana can provide a lot of relief to mothers during pregnancy. Anecdotal reports suggest that women are consuming cannabis for a variety of pregnancy ailments, including stress,  morning sickness, and even aiding ailments like hyperemesis gravidarum. Do the potential benefits outweigh the risks? That’s an extremely personal decision to make, and the research at this point is unclear. Though, when it comes to a baby, caution is always best.

What do you think? When it comes to prenatal marijuana use, are we being too cautious or not cautious enough? Share your thoughts with us on social media or in the comments section below. We’d love to hear from you!

Mar 28, 2016