Does Consuming Cannabis During Pregnancy Harm Your Unborn Baby?

Key takeaways.

Pregnancy is a sensitive time — not only does mum have extra needs while she’s turning gametes into a human, but there’s the little human to think about. In the world of medicine and pharmaceuticals, there’s an entire scheduling category for pregnancy. It means that one of the ways pharmacists categorise drugs is by how they affect pregnant women. Because it’s serious, sensitive, and there’s a wee-little life at stake. So what about cannabis use during pregnancy? 

Cannabis, until now, doesn't have a schedule with respect to pregnancy. Science has confirmed that the active compound in cannabis, THC, can move through the placental barrier and into the fetal bloodstream. But the evidence for what happens after that, or later on in the child’s development, is limited. For that reason, cannabis remains a no-no during pregnancy — but not because we know it’s harmful. It’s more because we don’t know that it’s not harmful.

That doesn’t mean that cannabis use during pregnancy is altogether uncommon. You’d be surprised how many women use cannabis during pregnancy for a variety of different reasons.

In this article, we’re going through some of the known dangers and known benefits of using cannabis during pregnancy, as well as some of the reasons that make this topic a hard one to research. Let’s check it out.

Why is cannabis use during pregnancy so understudied?

One of the first things that pharmaceutical companies typically have to do before releasing a medicine is assess its usefulness or caution during pregnancy. The medical industry acknowledges that pregnancy is a particularly sensitive time for both mum and baby, and not all medicines are conducive to a healthy pregnancy.

Why does cannabis lack this research?

To begin with, the body of scholarly cannabis research as a whole would have been much richer if we hadn’t abstained from cannabis research during prohibition. The second reason is that, since prohibition, cannabis was scheduled among the most dangerous drugs on the planet. The general consensus was that cannabis wasn’t good for anybody, ever.

Finally, collecting data about cannabis use during pregnancy, even now, is difficult because of the stigma associated with cannabis. For example, in this Californian study, researchers found that pregnant women were twice as likely to screen positive for marijuana during a drug test than they indicated in self-reporting. It’s obvious that there is some fear associated with revealing to your doctor that you use cannabis, especially if pregnant. In some parts of the world, screening positive to a drug test during pregnancy warrants a child abuse charge.

So it’s really important to talk about these limitations in research, which boil down to three main points.

For one, we never bothered to do such research in the past, although cannabis was used to assist child labour. Secondly, before we knew anything about cannabis, we labelled it as dangerous, and never fully acknowledged its therapeutic potential. And thirdly, the stigma surrounding it is still so strong, even in the legalization era, that some pregnant women are still too terrified to report cannabis use to their doctors. 

These are essentially the reasons why we can’t say with any certainty whether cannabis is dangerous to an unborn baby. And that’s a big problem - especially since there are still so many soon-to-be-mothers out there using it. 

What the science says.

One animal study that took place in 2012 investigated the effects of cannabis use in very early pregnancy. They found that it only took very slight changes in endocannabinoid levels to affect embryonic development. Activation or inhibition of endocannabinoid signalling at the CB1 receptor in pregnant mice altered the rate at which new placental cells formed and migrated. Scientists haven't replicated these results in humans. However, because of the similarities between the endocannabinoid systems of mice and humans, researchers concluded that cannabis use during early pregnancy could negatively affect embryonic development.

In another study conducted at the Christchurch School of Medicine, researchers took to studying women well into pregnancy. The researchers made an association between cannabis use during pregnancy and a detectably lower birth weight. Overall, babies of cannabis-using mothers weighed in, on average, 90g less than the babies of non-cannabis-using mothers. They considered this a statistically insignificant result. 

It’s worth comparing the Christchurch study to another one conducted in 1986. In the 1986 study, researchers found that white women who used cannabis regularly during pregnancy were more likely to have children with a lower birth weight than black women who used cannabis regularly during pregnancy. 

And lastly, in a study that compared alcohol, tobacco, and cannabis use during pregnancy, researchers found no association between cannabis use and symptoms of psychosis in offspring.

How culture and socio-economics plays into the research 

The aforementioned 1986 study is particularly interesting, because it shows a difference between races. Now, after cannabis legalization, we can definitely see a difference in the way that different races use cannabis. 

Another interesting study took place in 1989 by Dreher, and is often cited in relation to cannabis use during pregnancy. It was conducted on Jamaican women, many of whom smoked cannabis regularly. In fact, in Jamaica, it is common to smoke cannabis among members of the community as a way to strengthen bonds and connections.

Interestingly, researchers found that children of cannabis-smoking mothers displayed cries that were shorter in duration, they were more hoarse, and had a more variable frequency. It is thought that cries with these characteristics present in children who were exposed to perinatal risk, and they often express developmental disorders. 

However, the study observed this in cannabis-smoking mothers. If cannabis was delivered in a tea or otherwise, newborns expressed normal cries.

Dreher then went on to investigate further into the later development of children of cannabis-smoking mothers in Jamaica. Exposed neonates showed no significant birth weight differences compared to non-exposed neonates. When the infants were assessed for neonatal behaviour, there was initially no difference between the exposed and non-exposed. However, 30 days later, when assessed again, exposed infants’ scores were significantly higher on reflex and autonomic stability than their non-exposed counterparts. They were found to be less irritable and more social.

It’s important to realise the different cultural perspectives about cannabis use around the world, and how they manifest in different socio-economic situations. For example, in Jamaica, a  woman who smokes cannabis is more likely to have a tighter social circle, and is less likely to be socially or economically challenged.  However, in the USA, cannabis use is linked with lower educational achievements and a higher dependence on social welfare.

We can therefore consider the different socio-economic factors that play into the research results. According to the data presented, Jamaican cannabis-smoking mothers are more likely to come from higher socio-economic demographics. American cannabis-smoking mothers are more likely to come from lower socio-economic demographics. This might help to explain some of the variation in results, and how other factors play in.

Cannabis use during labour and midwifery

Needless to say, cannabis isn’t typically prescribed during child-labour. However, there is a lot of historical evidence that shows it was once used successfully during child-labour. Ethan Russo alludes to this kind of cannabis use in his book, Cannabis Treatments in Obstetrics and Gynaecology: A Historical Review.

It was also commonplace before prohibition for cannabis tincture to be stocked on shelves. It was most commonly prescribed for menstrual pain, morning sickness, and child-labour. 

How to make a real-life decision about your real-life baby

Okay - the jury is well and truly out. There are a few more studies out there, but they generally represent the same mixed bag of results. So it seems it’s really not that easy to measure the effects of cannabinoids on an infant. We do know that the endocannabinoid system is part and parcel of the fetal developmental process, and given that, cannabinoids must alter that function, even if only very slightly. 

So how do you make a decision?

The evidence suggests that there is only a really small likelihood your child will suffer if you ingest cannabis from time to time to deal with morning sickness or anxiety. However, that’s still just a suggestion. Plus, does having more make it worse? We don’t know.

It’s really important to weigh up the evidence, even if there’s not much of it. What are you using cannabis for, and how does that ailment stack up against the potential dangers? This is how you have to stack up the evidence.

Finally — you must talk to your doctor. A cannabis-friendly doctor should be able to guide you through those choices so that you can make the best decision for yourself and your baby. Don’t be shy to have conversations with experts and professionals. And if in doubt, cannabis can always wait until after childbirth.