New Study Reveals How Cannabis Affects Pregnancy

A new review of the medical and scientific literature surrounding cannabis and pregnancy, published this month in Obstetrics & Gynaecology, has concluded that “marijuana use during pregnancy is not an independent risk factor for adverse neonatal outcomes after adjusting for confounding factors.”

This is the latest contribution to a field of research that has often thrown up contradictory conclusions as to cannabis’ safety – or danger – during pregnancy. Back in June of this year, we reported on a study (which as usual had been badly misinterpreted by the Daily Mail) which suggested that, whilst cannabis use during pregnancy did seem to thicken an area of the infant’s brain known as the prefrontal cortex, it did not appear to effect the total brain volume, white matter volume, or grey matter volume, whilst tobacco use did.

Other studies, however, have suggested various negative outcomes for children exposed to cannabis in the womb. These include, but are not limited to, learning delays, tremors, ‘unusual emotional behaviour,’ depression, attention disorders, and a higher likelihood of skipping school.

This latest review of the available research suggests that, far from being down to cannabis use, these apparent harms are actually more likely to have been caused by other risk factors, such as tobacco and alcohol use. In many cases (although not all, of course), the mother’s cannabis use can in fact be seen as a symptom of wider social problems which are more likely to hold back the child’s development than the cannabis itself.

One of the key areas that the researchers were looking at in their review was the issue of low birth weight. A previous review, from the University of Arizona, had suggested that infants exposed to cannabis in the womb had 77% higher odds of being underweight at birth, and despite the author’s admission that causation had not been proven, and that many other factors were certainly involved, the idea that cannabis use causes low birth weights has persisted. This new review found no evidence that cannabis causes low birth weights in infants.

The biggest problem is that researchers have too often failed to adjust their findings to factor in things such as tobacco use, which is almost certainly associated with low birth weight, and which is strongly correlated with cannabis use, particularly in Europe. In other countries, however, tobacco use is far less prevalent, and studies in these places have shown significantly different results.

One of the first was undertaken in Jamaica in the late 60’s. Melanie Dreher studied 24 Jamaican infants exposed to cannabis prenatally, and 20 infants that were not exposed. Her findings showed no negative effects at all, and even suggested that the infants who had been exposed to cannabis were thriving. This was much to the dismay of the National Institute on Drug Abuse (NIDA), the famously anti-cannabis agency who had, until that point, funded the research. They withdrew funding soon after.

Perhaps what this new research shows us – other than that cannabis probably isn’t harmful to your unborn child, and is most likely safe to use as a treatment for morning sickness but probably shouldn’t be used to excess – is that things haven’t really changed all that much since the sixties. The conclusions of the research being carried out are still the same, but are still challenged by those who insist that poorly conducted studies are as valid as properly conducted ones. It seems unlikely that things will change, but as long as good research is being carried out the truth will continue, slowly, to seep through. Just don’t expect the Daily Mail to report it.

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