"Poison for the brain" : does smoking pot during pregnancy harm the baby??

Gynecologists warn of permanent consequences of cannabis use for the unborn child. Are the concerns justified?

Scientists advise against smoking pot during pregnancy

Smoked neat, mixed with tobacco or as a cookie: cannabis is the most widespread illicit drug in Germany – and probably the most tolerated as well. According to data from the European Drug Report, presented in June (PDF here), more than 27 percent of Germans aged 15 to 64 have used cannabis at some time.

But it’s another figure from the report that prompted the German Association of Gynecologists to issue a warning Tuesday: One in nine women in Germany between the ages of 18 and 34 has smoked pot in the past 12 months. This is the age at which most women become pregnant. According to studies, two to five percent continue to consume anyway. In the U.S., according to the latest figures, as many as one in 10 people grasps it. Pregnant women to a joint now and then, and quite a few do so almost daily (JAMA: Volkow et al., 2019). In this country, there are no exact numbers, but gynecologists believe there are more than assumed. The main reason they assume is that many think cannabis is a harmless drug that does not harm the child. But this is wrong. "As the unborn baby’s brain continues to develop from day to day, cannabis, just like alcohol, acts not simply as a drug, but as a poison", Says the president of the professional association Christian Albring.

Some women smoke pot for morning sickness

Cannabis is usually consumed as marijuana (dried flowers and leaves) or as hashish (the resin of the hemp plant pressed into blocks). Cannabis contains hundreds of ingredients. In smoking, there are additional toxins that are produced by burning the plants and the paper, and little or nothing is known about their effects.

Better researched is the substance group of cannabinoids, first and foremost delta-9-tetrahydrocannabinol (THC). This substance, which is found in the inflorescences, is also responsible for the effects on the psyche, such as the euphoric effect.

It occurs because THC can easily cross the cell barrier between the bloodstream and the brain. There, it docks at specific receptor sites (receptors) that are actually reserved for the body’s own cannabinoid system. This regulates processes in the body that have to do with memory, pain or nausea.

Thus, medical cannabis can also be used as a back-up medication for chronic pain or vomiting in the setting of cancer. Especially in the U.S., pregnant women also consume cannabis on their own for morning sickness. However, this effect has never been tested in a controlled study for ethical reasons. A Canadian observational study recently demonstrated that cannabis use during pregnancy results in women being less likely to develop gestational diabetes and less likely to experience pregnancy toxicity (preeclampsia) (JAMA: Corsi et al., 2019).

Cannabis can also be addictive, however, and studies also suggest an increased risk of psychosis and other mental illnesses.

The problem in pregnancy is that THC not only reaches the woman, but also the baby. This is because the substance can relatively easily cross the placental barrier, which is supposed to prevent harmful substances from reaching the child’s circulation.

Children whose mothers had smoked pot were particularly lightweight

When talking about the effects of cannabis in pregnancy, it is important to distinguish those that occur in the womb from those that start in pregnancy but sometimes are not apparent until years later, maybe never. "The study situation is generally poor", says Stephanie Padberg of the Embryotox pharmacovigilance center at the Charite hospital in Berlin.

THC is highly unlikely to cause deformities like those associated with alcohol. In a large study, however, scientists found a link between cannabis use by the mother and reduced fetal growth in utero (Journal of the American Academy of Child& Adolescent Psychiatry: El Marroun et al., 2009).

Particularly lightweight at birth were those infants whose mothers had smoked pot throughout pregnancy. The reason for this could be cannabis receptors in the placenta, which are stimulated by THC and lead to growth inhibition (Molecular Human Reproduction: Khare et al., 2006). In the SCOPE study from Australia, where cannabis is a widely used recreational drug, researchers attributed up to twelve percent of preterm births to THC contact in the womb (Reproductive Toxicology: Leemaqz et al., 2016). Another large Australian study concluded that infants exposed to THC were more likely to require treatment in an intensive care unit after birth (Addiction: Burns et al., 2006). However, they did not find increased mortality.

THC causes minor blackouts in the brain

Also withdrawal symptoms, as they occur in newborns whose mothers used heroin during pregnancy, usually do not occur in babies of cannabis smokers. If anything, doctors tend to find subtle abnormalities. For example, children sometimes show exaggeratedly strong reflexes, cry in high-pitched tones, or have disturbed sleep patterns. Scientists see this as a sign that cannabis consumption during pregnancy not only affects the growth of the children, but also their brains.

This is where a particularly large number of cannabinoid receptors are located; almost 90 percent of cells have such docking sites. They are formed at a very early stage – and are extremely important for the networking of nerve cells. Accordingly, they react sensitively if they are disturbed in the process. "The processes involved in brain development can be thought of as occurring in a telephone switchboard", explains Tibor Harkany from the Medical University of Vienna.

Every cell in the brain, he said, is at 40.000 others, according to the neuroscientist. During brain development, cells would learn which of the incoming information is important to them and which they can ignore. "THC interferes with this process, causing minor blackouts in telephone exchanges."

They can last up to 48 hours, according to Harkany. In the worst case, "emergency calls" would then be made Turned down and unimportant background noise loudly. The brain remembers this wrong pattern – and does so for the rest of life.

The neuroscientist is convinced that these effects later affect children’s learning and psyche. Changes he has studied primarily in animal models, researchers from the Netherlands also wanted to demonstrate in humans.

Using magnetic resonance imaging, they were able to show that the brain structure of six- to eight-year-old children whose mothers used cannabis during pregnancy looked different from that of unexposed children: In particular, the anterior portions of the cerebral cortex were thickened (Biological Psychiatry: El Marroun et al., 2016). There, in the prefrontal cortex, processes are controlled that are important for attention, self-control and working memory.

Can the children later remember things more poorly?

But what does that mean for the children? Does cannabis use during pregnancy really affect whether a child is less attentive later on or has trouble remembering things?? Some observational studies make such a connection.

In the first few years, the children are initially inconspicuous, they say. But from school age onwards, this would change. In studies, some of them performed worse in language and memory tests and were more inattentive than their schoolmates who had not been exposed to the drug in the womb.

Some changes may persist beyond childhood into adolescence, according to studies, including impulse control disorders, childhood depression, addictive behavior, and later delinquency. Some effects, Harkany said, can be explained by the fact that there are particularly high numbers of cannabis receptors in brain areas related to reward, addiction and motor control.

Cannabis is not responsible for everything

However, all these studies have a problem: They cannot determine exactly how much of the child’s changes are due to cannabis. "Often, women who use cannabis heavily and regularly also use other drugs such as alcohol and tobacco", says Stephanie Padberg from Embryotox. Poorer prenatal care and difficult social situations could also affect child development. That’s why, she says, you have to be careful in interpreting the results.

Presumably, the effects on the child also depend on the amount of intoxicant consumed. So it probably makes a difference whether someone smokes a joint once in the fifth week or smokes pot every day. That cannabis is as toxic to the child as alcohol – drinking during pregnancy is the most common cause of mental retardation – is unlikely in any case.

"Ultimately, we have no evidence so far that cannabis is highly toxic to the unborn, but none to give the all-clear either,", says Padberg. Therefore, she says, women should be clearly discouraged from continuing to use during pregnancy and breastfeeding – whether once or regularly.