So Does Using Marijuana In Pregnancy Hurt A Baby Or Not?
As more states legalize medical marijuana and recreational marijuana, questions about the drug’s effects on a fetus will become a more central public health concern. One significant flaw with most studies looking at marijuana use in pregnancy is that researchers do not take into account that a large proportion of marijuana users also smoke tobacco. Since negative effects from smoking during pregnancy are well-established, it could be that these outcomes are the ones being detected when researchers study marijuana use in pregnancy without adjusting for the effects of smoking.
The findings of a new study would seem at first to allay any concerns about that flaw: after adjusting for tobacco use, a combined analysis of more than two dozen studies found no increased risk of low birth weight, preterm birth or a handful of other poor outcomes among newborns whose mothers used marijuana during pregnancy.
But a closer look reveals the same problems that have plagued previous attempts to investigate all the research to date: there simply are not enough high-quality studies that provide enough data on enough pregnancies to separate out all the possible effects that could interfere with identifying effects from marijuana.
“When the authors go from the adjusted analyses to the further adjusted analyses, they have to dramatically reduce their sample size,” noted Aaron Caughey, MD, chair of the Department of Obstetrics and Gynecology at Oregon Health & Science University in Portland. “Thus, the negative findings of no increased risk for preterm birth or low birthweight could just be because of inadequate study power.”
It’s also important to note up front that this study, published in Obstetrics & Gynecology, focused only on a handful of possible risks at birth and only at birth. “We did not investigate long-term neurodevelopmental outcomes after exposure to marijuana in utero, and further study is warranted in this regard,” the authors wrote. In fact, few studies exist at all that look at long-term effects of marijuana use during pregnancy, and of the handful that do, which Emily Willingham and I analyzed for our book’s section on marijuana use, almost none take into account the use of tobacco, alcohol or other drugs, making it hard to know what effects from marijuana, if any, exist.
An activist smokes a marijuana joint prior to marching in the annual Hemp Parade (Hanfparade) on . [+] August 13, 2016 in Berlin, Germany. (Photo by Sean Gallup/Getty Images)
That lack of research is problematic given the drug’s prevalence. An estimated 2% to 27% of women use marijuana during pregnancy, but the number is hard to pin down because it’s almost certainly underreported due to stigma. Estimates also vary among different populations and according to how “use” is defined and how it’s detected.
Shana Conner, MD, of Washington University School of Medicine in St. Louis, and her colleagues combed six databases of medical research up through August 2015, eventually ending up with 31 studies ranging from 1982 through 2015 that met their criteria. They only included observational cohort and case-control studies in which they could separate the data on marijuana use from other substance use, including tobacco.
Among the 31 studies, 68% were conducted in the U.S. Together, the studies included 7,851 women who used marijuana during pregnancy and 124,867 who did not. Use of marijuana was based on either self-reporting from the mothers or from objective testing of the meconium, umbilical cord, urine, saliva or blood. The study did not distinguish between smoking marijuana and other forms of use, such as ingestion. (Almost no published studies examine ingested marijuana outcomes.)
The researchers primarily focused on outcomes of low birth weight (less than 5.5 lbs) and prematurity (born before 37 weeks of pregnancy), because these are the outcomes most often studied and because they are the most likely outcomes at birth based on what we know about the body. However, the authors also attempted to calculate the risks of stillbirth, miscarriage, being admitted to the neonatal intensive care unit (NICU) or a Level II nursery, low Apgar score, placental abruption, death during delivery and infants being underweight for their gestational week of birth.
Before making any adjustments for tobacco use or frequency of marijuana use, infants born to women who used marijuana were more likely to arrive early or have a low birth weight: 15% of marijuana-exposed newborns compared to 10% of newborns whose mothers didn’t use marijuana. But this increased risk dropped to statistical insignificance when the authors made either of two adjustments: distinguishing between women who used marijuana less than once a week versus those using it more often, or adjusting for tobacco use along with marijuana use. In both cases, using marijuana less than weekly or without tobacco did not lead to a greater risk of preterm birth or low birth weight. Using marijuana at least once a week doubled the risk of preterm birth or low birth weight.
When the authors analyzed all the numbers together from the seven studies that separately reported tobacco use and marijuana use, no increased risk of preterm birth or low birth weight showed up among those who used marijuana but didn’t smoke cigarettes. Similarly, after adjusting for tobacco use, the risk of placental abruption or an underweight newborn were no greater for newborns whose mothers used marijuana than for mothers who didn’t. Although the risk of a lower average birthweight, stillbirth or a low Apgar score was increased among infants exposed to marijuana, the researchers did not have enough data to calculate these risks after adjusting for tobacco smoking.
Again, that pesky problem of limited data means it’s hard to draw many strong conclusions from this study except that more higher-quality studies need to be done.
“I would remember that at baseline, all of the existing analyses have generally found increased risks of pregnancy complications,” said Caughey. “The current study finds that these risks are attenuated but cannot definitively state that there is no negative impact on the developing fetus.” Further, no current evidence suggests that there are beneficial effects from marijuana use during pregnancy, he said.
One requirement to determining whether exposure to a substance can cause a problem in the body is that a biological mechanism exists: there needs to be a clear path showing how the substance can have a direct, physical effect based on what we know about the body. In the case of marijuana, at least some possible biological mechanisms have already been identified. For example, the compound delta 9 tetrahydrocannabinol in marijuana easily crosses the placenta and remains in the adult body for up to 30 days, so its ability to reach the fetus and remain there means it could potentially affect fetal development. Past research has also found carbon monoxide levels in the blood after smoking marijuana were five times higher than levels after smoking tobacco. High levels of carbon monoxide in the blood could impede adequate oxygen levels in the blood, which could affect the fetus as well.
But data from large studies need to show possible effects, and the ones available aren’t adequate. For example, these authors found some evidence suggesting that more frequent use of marijuana did increase several risks at birth, but women who use more marijuana are also likely to smoke more and use other drugs, and the authors didn’t have enough information to separately analyze that.
So again, the biggest limitation to the whole analysis is that the studies included did not contain enough data for enough infants to reliably calculate risks for many of the outcomes the authors wanted to look at. That, combined with the lack of data (but theoretic risk) on neurodevelopmental outcomes or other long-term effects, means there is far too little evidence to say that marijuana in pregnancy has no negative effects.
“Alcohol and cigarettes were legal and used during pregnancy for many years and caused untold damage to developing neonates,” Caughey said, referring to fetal alcohol spectrum disorders and to effects from tobacco such as fetal growth restriction, stillbirth and preterm birth.
“Marijuana as a hallucinogenic drug that is inhaled has the potential to cause all of the problems seen in both of these legal drugs,” Caughey continued. “I would strongly recommend that all women using marijuana quit before attempting to get pregnant or when they learn they are pregnant.”
New findings suggest prenatal marijuana exposure doesn’t increase birth risks—but that’s not the whole story.
Using cannabis ‘can lead to miscarriages’
Women risk losing their babies if they smoke cannabis at the time of conception or early in pregnancy, according to a study published yesterday.
Cannabis is the most widely-used illegal drug among women of childbearing age. Scientists studying mice have found that THC, the active ingredient in the drug, can retard embryo development and prevent it from reaching the womb.
The findings suggest that smoking cannabis may lead to miscarriages caused by embryos developing outside the womb, in the fallopian tubes.
Writing in the Journal of Clinical Investigation, the team, led by Dr Haibin Wang and Dr Sudhansu Dey from Vanderbilt University in Nashville, Tennessee, warned: “Our observation of … mice exposed to excessive THC raises concern that the adverse effects of maternal use of marijuana could be seeded very early in pregnancy.”
THC, or tetrahydrocannabinol, binds to two receptors in the brain called CB1 and CB2. Receptors are proteins into which other molecules fit like a key in a lock. Biological processes are triggered when molecules bind on to receptors.
THC activity in the brain leads to the “high” enjoyed by cannabis users. But CB receptors are also found in sperm, eggs and newly-formed embryos.
During early pregnancy, a naturally-occurring molecule called anandamide normally activates these receptors and the team found that anandamide levels are carefully balanced to maintain normal embryonic development.
When pregnant female mice were exposed to THC, the drug had the same effect on the CB1 receptor as anandamide and swamped the finely-tuned signalling system.
The researchers found that this, in turn, led to embryos remaining in the fallopian tubes instead of becoming implanted in the womb as nature intended. “Embryo retention in the fallopian tube is a significant cause of ectopic pregnancy, the incidence of which has markedly increased during the past decade,” they wrote.
Embryos recovered from the treated mice also showed signs of apoptosis – a natural process by which defective cells destroy themselves.
In an accompanying commentary Dr Herbert Schuel from the State University of New York points out that a number of drugs used to suppress appetite or trigger weight-loss also affect anandamide signalling and, therefore, need to be carefully monitored.
Using cannabis ‘can lead to miscarriages’ Women risk losing their babies if they smoke cannabis at the time of conception or early in pregnancy, according to a study published yesterday.