Children exposed to cannabis in the womb do not show signs of impaired cognitive or language development by age three, according to new research that challenges concerns about prenatal cannabis use.
The study, published in the journal Early Human Development, found that children with prenatal cannabis exposure actually scored higher on language assessments than unexposed children, and performed equally well on cognitive tests.
Recent data shows that past-month cannabis use amongst pregnant women in the US has grown from 3.8% in 2002 to 7% in 2017, and daily use during pregnancy increased from 0.9% to 3.5% in the same period.
This prompted the multi-national team of researchers from King’s College London, Cambridge University, Aalborg University, and the University of Oslo to hypothesise that children exposed to cannabis while developing in the womb would develop cognitive and language issues by the age of three.
The study analysed data from Danish families registered with Familieambulatorier (Family outreach clinics), which continuously monitor children of families deemed vulnerable or high-risk from early pregnancy until the child reaches school age.
The cohort consisted of 810 Danish children born between the years of 2009 and 2015 who were not diagnosed with conditions such as foetal alcohol syndrome or epilepsy, as these conditions would negatively affect the outcome of language and cognitive assessments.
Children were split into four groups, based on their exposure during gestation. 106 (13%) were exposed to cannabis only, 138 (17%) were exposed to tobacco only, 112 (14%) were exposed to both, and 454 (56%) were registered as not being exposed to either substance.
Researchers found that children with prenatal cannabis exposure achieved a higher Bayley-III Language scale score of 3.26-points than those in the group who were not exposed to cannabis, and they found that exposure to tobacco did not worsen this outcome.
Language scores were seen to rise slightly more within all three of the exposed groups in the cohort than the non-exposed control group as the children got older, although the researchers made it clear that this data could hold “limited clinical significance”.
The study also revealed that children within all three of the exposed groups in the cohort performed as well as children in the unexposed control group on the Bayley-III Cognitive scale assessment.
“The current study is, to the authors’ knowledge, the first to investigate the association between prenatal co-exposure to cannabis and tobacco, relative to either drug alone, and cognitive and language outcomes in young children,” the study said.
“Contrary to our pre-registered hypotheses, children with prenatal cannabis exposure had higher scores on the Bayley-III Language scale, and children with prenatal exposure to cannabis and tobacco had a greater age-related increase in language scores, compared with the other groups. There were no group differences on the Bayley-III Cognitive scale. In short, we found no evidence that prenatal exposure to cannabis was associated with impaired cognitive or language development, and no evidence that the combination of cannabis and tobacco was associated with worse outcomes compared with either drug alone, in this sample of high-risk children.”
These new findings are similar to those of a previous study, which found that children exposed in utero to cannabis had better developmental scores at age two than those who weren’t exposed, although this difference had disappeared by the following year’s assessments.
The authors of the current study stressed that their findings do not mean cannabis is safe to consume during pregnancy, and that it is “unlikely” that doing so causes children to have better cognitive or language skills than those who were not exposed. Their findings, they say, could be linked to the familial and societal environments the children are brought up in.
“It is unclear why children in the cannabis and cannabis + tobacco groups were slightly better off on language development compared with the other groups. We consider it unlikely that this was due to a salutary effect of cannabis on neurocognitive development and speculate instead that this could have to do with unmeasured factors that may have differentiated the family and social environments of children in the four groups,” the study said.
