More pregnant women are using marijuana. We don’t know if that’s safe.
And cannabis dispensaries are marketing their products to pregnant women for morning sickness.
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In a California study, the percentage of pregnant women who screened positive for marijuana use by self-report and/or a positive toxicology test increased between 2009 and 2016, from 4 percent to 7 percent. Getty Images/EyeEm
Soon after Amy Smith* started thinking about having a baby a few years ago, she wondered what she’d do about her marijuana habit.
Smith had deployed twice with the US Army, and had returned from Iraq with severe post-traumatic stress disorder. At one point, her doctors at the VA had her taking 22 pills to help her sleep and quell her depression and anxiety.
Then she discovered marijuana. Smith went off all the prescription medication and began self-medicating by smoking cannabis. “It was amazing — how it helped me get out of bed. I wasn’t terrified of being at the grocery store anymore. I wasn’t on the verge of losing my mind.” (A resident of Utah, the drug only became legal for medical use last November.)
In 2014, Smith became pregnant with her first child. And after Googling studies about the risks, “dancing around the topic” with her doctor, and having many long and difficult discussions with her husband, she decided to use marijuana 4 to 5 times per week while pregnant and while breastfeeding.
“When my anxiety showed up when I was pregnant, I knew what I was in for,” she said. “I could pile up the medications [and] eventually end up in hospital. I chose marijuana instead.”
The marijuana landscape is rapidly changing in the US. Weed has been legalized in 32 states for medical purposes, in 10 states plus DC for recreational use, and cannabis is being marketed directly to pregnant women for morning sickness. And now more and more women are grappling with the question Smith faced: whether to use while pregnant.
The American College of Obstetricians and Gynecologists advises doctors to screen for marijuana use in pregnant women and encourage users to quit — even in cases when weed is being used for medicinal purposes — while carrying and breastfeeding.
“There are many concerns about prenatal marijuana use and the potential for adverse effects on the fetus,” said researcher Kelly Young-Wolff of the Kaiser Permanente Northern California Division of Research. “And although the health effects of prenatal cannabis use are complex and not well understood, no amount of cannabis has been shown to be safe during pregnancy.”
Despite that, Smith is part of a growing, but still small, group of women who are opting in. Aside from her husband, she just hasn’t told a soul about it because, according to her, “It’s too much of a risk socially and legally.”
Marijuana use among pregnant women in California doubled between 2009 and 2016
There’s no official screening system at the state or federal level for marijuana use in pregnancy in the US. And in many states, substance use during pregnancy is sufficient to make a child abuse or neglect report.
California a rare exception. And the best evidence on marijuana use while carrying a baby comes from Kaiser Permanente Northern California: It’s the only large health care system in the US that screens all pregnant women for prenatal marijuana use as part of standard prenatal care by urine toxicology and self-report. This means they have an objective way to measure whether it’s increasing or decreasing instead of relying solely on women’s self-reports.
In a study of that data, by Young-Wolff and her colleagues at Kaiser, they found a near doubling in the percentage of pregnant women who screen positive for marijuana use by self-report and/or a positive toxicology test between 2009 and 2016, from 4 percent to 7 percent.
Notably, the prevalence of marijuana use in their hospital system was nearly twice as high by toxicology testing versus what women reported to their doctors, suggesting that it’s probably more common during pregnancy than many people admit.
Trends in self-reported and biochemically tested marijuana use among pregnant Females in California From 2009 to 2016. JAMA
Weed was especially popular among younger moms: 22 percent of pregnant women under the age of 18, and 19 percent aged 18 to 24 years, screened positive for marijuana use in 2016, which shows that the younger generation may rely more heavily on marijuana during pregnancy. And Young-Wolff says the data from her hospital system reflects the national survey data we have on marijuana use during pregnancy, which also shows it’s going up.
It seems like this shift has something to do with with the swift changes in marijuana law and culture in recent years. In the November midterms alone, three more states decided to legalize recreational or medical weed. And dispensaries in places where weed is legal often market it directly at pregnant women. In a recent study on recommendations to pregnant women at Colorado cannabis dispensaries, researchers found the majority (69 percent) peddled products to treat morning sickness, and 36 percent told women the drug is safe to use in pregnancy.
Another study by Young-Wolff’s team at Kaiser Permanente found pregnant women with severe nausea and vomiting had four times greater odds of marijuana use than women without a nausea and vomiting diagnosis — though it wasn’t clear whether their morning sickness led them to use weed or weed exacerbated their morning sickness.
Either way, the marketing materials on cannabis products often omit an important point, Young-Wolff said: There’s a lot we don’t understand about marijuana’s health effects generally — and, in particular, on moms and babies, including the drug’s potential risks in pregnancy.
The hazy evidence on smoking weed in pregnancy
Since the late 1980s, researchers have known that THC — the active ingredient in cannabis — can cross the placenta and reach the fetus. More recently, researchers have found that THC is also secreted in breast milk up to six days after the last use. So that means the fetus is exposed to THC, and the concerns about marijuana’s health effects during pregnancy and lactation stem mainly from this fact.
One of the best summaries of the evidence on the health effects of cannabis comes from a major report out of the National Academies of Sciences, Engineering, and Medicine. More than a dozen experts reviewed more than 10,000 studies published between 1999 and 2016. (Most of the data in the review focused on smoked marijuana.)
Overall, the report suggested weed shows promise for chronic pain, multiple sclerosis, and cancer patients — but it also complicated the narrative that weed is a safe drug. The report found that it may increase the risk of respiratory problems (when smoked), schizophrenia and psychosis, getting into car accidents, and lagging social achievement. The report also uncovered pregnancy-related problems. In particular, the strongest link they uncovered showed that babies exposed to cannabis in utero tended to have lower birth weights.
“But what we couldn’t say is whether that’s a direct effect of marijuana or of smoking,” explained Marie Clare McCormick, a professor of maternal and child health at Harvard and chair of the National Academy of Sciences (NAS) committee that put out the report. The researchers noted that the marijuana birth weight findings were consistent with the effects of cigarette smoking on fetuses. McCormick explained that smoking any substance increases carbon monoxide in the blood, which reduces blood’s oxygen-carrying capacity, so not as much gets to the baby.
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“Clearly you can say, ‘Don’t smoke during pregnancy no matter what you’re smoking.’” But for the remainder, it’s the precautionary principle: Until we know more you probably shouldn’t do it,” McCormick summed up.
The NAS report drilled down into other health effects during pregnancy, like whether the babies of moms who used marijuana are more likely to wind up in the NICU or experience sudden infant death syndrome and cognitive and academic achievement challenges later in life. And on these important questions, it was equivocal: The researchers found “limited, insufficient, or no evidence.”
Still, the American College of Obstetricians and Gynecologists say that there are no approved indications or recommendations regarding prenatal marijuana use — even though the impact of prenatal cannabis use isn’t yet fully understood.
Even so, Young-Wolff said. “[There’s] sufficient evidence [of] an association between prenatal marijuana use and lower offspring birth weight, and limited research shows a correlation with some developmental delays or difficulties with executive functioning in the child — like problems with impulse control and attention.” And that’s enough to make health professionals wary.
Why marijuana bump science is so shaky
There are a few reasons why the research base on marijuana in pregnancy is so limited and inconclusive. Again, most of the evidence we have on weed’s health impact on the fetus comes from research on smoking — and there are many different ways people ingest cannabis nowadays, through edibles, oils, and vape devices to name just a few.
The THC content in weed has also shot up dramatically, which means it may be riskier to use while pregnant. So, as Young-Wolff of Kaiser told me, “A lot of the research that has been done is quite old” and doesn’t reflect the current marijuana landscape or the THC levels in today’s products.
The studies out there also tend to be small, without enough statistical power to accurately detect relationships; they often rely on self-reported data, which is flawed when it comes to substance use. A lot of the research also didn’t control for “confounding factors” or all the non-weed variables that may bias the results of studies.
“Pregnant marijuana users often use other drugs in pregnancy,” Young-Wolff explained, “and prior studies haven’t been able to differentiate which effects are due to marijuana or other drugs they may be using.”
Finally, the federal government still classifies marijuana as a Schedule 1 substance — the same legal and regulatory league as heroin — and that means researchers need to jump through all kinds of hoops to run studies.
The National Academies called for these restrictions to be relaxed so we can get a better understanding of the effects of marijuana in all kinds of different vulnerable groups. Erin Parker,* another weed-smoking mom, agreed. “I think it’s absurd to be passing laws making a drug legal and not having research on whether or not it’s safe for pregnant women.”
“They just need to reschedule [weed] so that it can be researched,” Smith reiterated. “If medical research came out and told me there were significant risks to my kids’ long-term health and development, I would listen to that research. But for now, like mothers have done since the beginning of time, I’m doing the best I can.”
*These names have been changed to protect the identity of the women.
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The Effects of Marijuana on Fetal Development
The Effects of Marijuana on Fetal Development
Given that many states have or are now moving forward with the legalization of medical and recreational marijuana, it should be no surprise that we are seeing an increasing number of women in our clinic who are using marijuana on a regular basis. According to a nationwide survey, 7.3% of Americans 12 or older regularly used marijuana in 2012 , up from 5.8% of Americans in 2007. Among younger and socioeconomically disadvantaged women, prevalence of marijuana use is even higher, in the range of 15 to 28 percent.
The majority of marijuana users are young and of reproductive age. It is estimated that roughly half of female marijuana users continue to use during pregnancy . These changes in the prevalence of marijuana use raise important questions about the effects of marijuana use during pregnancy on embryo development. At th is point in time, the data, though limited, suggests that marijuana use during pregnancy is associated with elevated risk for miscarriages, birth defects, developmental delays, and learning disabilities. Animal data supports these findings and suggests even further potential for developmental issues. Researchers at Georgetown University Medical Center summarized the adverse outcomes associated with marijuana use during pregnancy and linked those outcomes to specific molecular signaling pathways (1). It is one of the most comprehensive review papers on marijuana effects during pregnancy to date and provides clinicians with information which can be used to discuss the risks of using of marijuana during pregnancy.
Metabolism of THC as it Relates to Pregnancy:
THC, the main psychoactive component of marijuana, has a half life of 8 days in fat and is detectable for up to 30 days in the bloodstream. Once circulating in the bloodstream, THC is readily able to cross the blood brain barrier and the placenta due to its lipophilic nature. In a primate study, THC was detectable in fetal blood just 15 minutes after intravenous infusion in the mother. Three hours following infusion, fetal blood levels of THC equilibrated to maternal blood levels (2). A separate study in canines found that THC was deposited in fetal fat at concentrations that are approximately 30% of maternal plasma levels (3). Given the pharmacokinetic properties of THC, maternal tissues act as a reservoir for THC and other cannabinoids which results in prolonged fetal exposure. Taken one step further, when marijuana is used occasionally during pregnancy, say once per month, fetal exposure to marijuana persists throughout the fetus’ entire development in the womb.
Marijuana Administration and THC Dosage:
Typically, marijuana is inhaled (through smoking or vaping) or consumed in edible form. Inhalation results in rapid drug delivery and onset of physiological effects, whereas oral consumption is associated with a slower and lower peak THC concentration. Dosages of THC are difficult to assess through clinical interview when a patient reports smoking because drug exposure varies according to smoking topography (the number, length, depth, and volume of inhalations). Dosages of THC in commercially available edibles are much more straightforward.
It is also important to note that older research on the effects of marijuana on embryo development is not reflective of today’s typical dosages. The National Institute on Drug Abuse maintains a program to track THC potency and has found that THC levels in marijuana have increased nearly 25-fold since the 1970s (4).
How Cannabinoids Act Upon the Brain:
Cannabinoids mainly act upon two prominent G protein-coupled receptors: CB1 and CB2 . CB1 receptors are present in high levels in the brain and gonads (testes and ovaries) whereas CB2 receptors are more sparse and are found in immune cells and some neuronal cells (5). Endogenous cannabinoids produced by the human body interact with these receptors and current data indicate that the endocannabinoid system plays a role in the regulation of sleep, feeding, pain, learning, and memory.
It is thought that the psychoactive effects of THC are a result of binding (partial agonist) to CB1 receptors in the brain. Under homeostatic conditions, cannabinoid signaling is involved in a number of important, tightly regulated processes that are necessary for healthy embryo development. Disruption of these tightly regulated signaling pathways by exogenous cannabinoids may have a number of downstream adverse effects on: (1) Obstetrical Outcomes (ie., preimplantation and implantation), and (2) Embryo Development (ie., direct effects on the fetus).
How Cannabinoids Affect Obstetrical Outcomes:
Implantation, the attachment of the fertilized egg to the uterine wall, is dependent upon a number of tightly regulated processes. Evidence suggests that there are five ways in which cannabinoids can affect implantation:
- Impairment of Fallopian Motility: Cannabinoid signaling controls muscle contraction and relaxation in the fallopian tube responsible for the movement of a fertilized egg through the fallopian tube and into the uterus.
- Ectopic Pregnancy: Previous studies have shown that the blood collected from women who have had ectopic pregnancies contains significantly higher levels of the naturally occurring cannabinoid, anandamide, compared to normal pregnant controls. Consistency between human and animal data adds confidence that the observed findings in animal models of altered cannabinoid signaling may play a role in ectopic pregnancy.
- Non-Hatched or Non-Viable Embryo: In mice models known to have altered cannabinoid signaling, an increased mortality of offspring was observed in association with implantation of slowly developing embryos (6).
- Decreased Uterine Receptivity: It is theorized that the binding of exogenous cannabinoids to CB1 receptors in the uterus has embryotoxic effects on the uterine environment. Modeling of this scenario has halted the development of blastocysts in vivo and in vitro (7) .
- Miscarriage (Spontaneous Abortion): Folic acid (Vitamin B9) is essential for embryo development and cannot be synthesized by the body which is why women are encouraged to take folic acid supplements during pregnancy. THC significantly decreases fetal folic acid uptake. Low levels of folic acid during pregnancy are associated with higher rates of miscarriages, as well as neural tube defects and low birth weight.
How Cannabinoids Affect Embryo Development:
THC crosses the placenta, enters fetal blood circulation, passes through the blood brain barrier, and is found at the highest levels in fetal fat tissue. The brain is 60% fat and therefore stores THC following maternal ingestion. The brain is also densely populated with CB1 receptors which mediate THC’s psychoactive properties.
- Folic Acid Uptake: As stated above, THC interferes with fetal folic acid uptake. Low levels of folic acid during pregnancy are known to be associated with neural tube defects and low birth weight.
- Cellular Growth: Exogenous cannabinoids may interfere with critical pathways for cellular growth and angiogenesis (formation of new blood vessels).
- Neural Development: Cannabinoids acting upon the CB1 receptor have the ability to influence the differentiation of neural cells from stem cells in the brain. This has tremendous potential to negatively affect learning and memory as well as developmental processes such as limb development.
Usually we take a balanced approach to the use of medications during pregnancy: Does the potential benefit of taking a particular drug outweigh the risks of fetal exposure to that drug or the effects of untreated disease in the mother? At this point, there is no compelling evidence to suggest that marijuana is an effective treatment for any mental health disorders. Given that a number of adverse outcomes are associated with marijuana use during pregnancy , the risk benefit decision seems straightforward: the benefits do not outweigh the risks.
Why Do Women Use Marijuana During Pregnancy?
Many women view marijuana as a relatively benign drug and are not aware that its use poses any health risks. Given the dearth of information on the reproductive safety of cannabis and the potential risk for adverse outcomes, the American College of Obstetricians and Gynecologists (ACOG) has issued a committee opinion on the use of marijuana in pregnant and nursing women, calling for OB-GYNs to educate and urge their patients who are pregnant or contemplating pregnancy to discontinue marijuana use.
But what about the women who use marijuana to help them manage various psychiatric symptoms, including depression and anxiety? Some of these women may choose to use marijuana over traditional psychiatric medications during pregnancy. Is it because women want to avoid psychiatric medications during pregnancy? Is psychiatric care too difficult to find or too expensive? My guess is that there a number of factors at work here.
If the issue is wanting to avoid pharmacologic treatments during pregnancy — that’s a personal choice, to be made ideally with medical supervision. However, if that is the case, marijuana cannot be viewed as a substitute. Some women mistakenly believe that marijuana is safer than psychiatric medications because it is ‘natural’. Conventional antidepressants, including SSRIs, have a plethora of efficacy and reproductive safety data to support their use during pregnancy, marijuana does not. A lack of information does not make marijuana safe nor do recent changes in legislation.
Wanting to avoid pharmacologic treatment for mental health disorders during pregnancy is common. If that is the case, we can encourage women to explore non-pharmacologic treatment modalities, such as cognitive behavioral therapy which has so much efficacy data at this point and has no side effects.
If the barriers are due to provider access and cost, that is much more difficult to rectify. We have an obligation to offer effective and safe treatments for mental health disorders so that we can have healthier moms and babies. While we can’t control the direction of federal funding for healthcare or medical research, efforts are being made that bypass these traditional pathways. One approach is to empower primary care physicians to deliver effective mental health care, and technology is being leveraged to offer free or low cost web-based therapy that may allow people to access care they couldn’t have before.
As legislation for medical and recreational marijuana is changing, marijuana is becoming more accessible and acceptable. Unfortunately, it will take years for research to catch up with use. The information available now warrants a cautious approach with regard to marijuana use during pregnancy and underscores an urgent need for more human data.
Alexandra Z. Sosinsky
- Friedrich J, Khatib D, Parsa K, Santopietro A, Gallicano GI. The grass isn’t always greener: The effects of cannabis on embryological development. BMC Pharmacol Toxicol . 2016 Sep 29; 17(1):45.
- Martin BR, Dewey WL, Harris LS, Beckner JS. 3H-delta9-tetrahydrocannabinol distribution in pregnant dogs and their fetuses. Res Commun Chem Pathol Pharmacol. 1997;17(3):357-70.
- Bailey JR, Cunny HC, Paule MG, Slikker WJ. Fetal disposition of delta-9-tetrahydrocannabinol (THC) during late pregnancy in the rhesus monkey. Toxicol Appl Pharmacol. 1987;90(2):315-21.
- Psychoyos D, Hungund B, Cooper T, Finnell RH. A Cannabinoid Analogue of 3H-delta9-tetrahydrocannabinol Disrupts Neural Development in Chick. Birth Defects Research. 2008;83:477-488.
- Mackie K. Cannabinoid receptors: where they are and what they do. J Neuroendocrinol. 2008;1:10-4.
- Paria BC, Song H, Wang X, Schmid PC, Krebsbach RJ, Schmid HH, Bonner TI, Zimmer A, Dey SK. Dysregulated cannabinoid signaling disrupts uterine receptivity for embryo implantation. J Biol Chem. 2001;276(23):20523-8.
- Schmid PC, Paria BC, Krebsbach RJ, Schmid HH, Dey SK. Changes in anandamide levels in mouse uterus are associated with uterine receptivity for embryo implantation. Proc Natl Acad Sci USA. 1997;94(8):4188-92.