Cannabis legalisation not linked to adverse birth outcomes – study

Legalisation of cannabis in the US is not linked to any significant adverse outcomes for  child health, according to a recent study.

New data shows that changes in legal status of cannabis in US states is not associated with increases in adverse clinical birth outcomes.

Researchers at Purdue University studied the relationship between the liberalisation of state-level cannabis laws and two key indicators of child health – birthweight and gestational age.

Their findings were published in the journal Population Research and Policy Review.

While the authors reported a trend which indicated a reduction in average birthweight and gestational age for some groups of women following the relaxation of cannabis penalties, they acknowledged that these changes were not linked to any “increases in clinically meaningful birth indicators associated with adverse child health.”

The findings are similar to those reported in a 2021 study which found “no statistically significant effect of medical cannabis laws on the proportion of newborn hospitalisations”. 

The authors concluded: “Our findings indicate that cannabis policy liberalisation may be contributing to lower average birth weights and reduced average gestational age, but not in a manner that has increased low birthweight (<2500 g) infants or preterm (<37 weeks) births. 

“These results indicate that while cannabis policies have not led to increases in adverse clinical birth outcomes overall, these trends are worth monitoring to ensure that increases in clinically relevant child health outcomes do not emerge as the nationwide trend toward liberalised cannabis policy persists. “

They added: “Although our study does not show substantial changes in adverse birth outcomes, policymakers should be attentive to opportunities to strengthen child health by considering policies that minimise consumption, particularly heavier forms of consumption, by prospective parents.”

While the evidence base around the effects of cannabis use during pregnancy on perinatal is growing, studies assessing the potential impacts of cannabis exposure are mixed.

Some observational data has identified a link between exposure and low birth weight and/or an increased risk of preterm birth. However others have failed to substantiate these claims once adjusting for other factors, such as tobacco smoking.

The majority of the existing studies have been done on recreational cannabis, accessed through the illicit market, which tends to contain higher levels of THC than that in medicinal cannabis.

There have been very limited, if any, studies exploring the effect of prescribed cannabis on perinatal health, as advice from clinicians is that women should refrain from using cannabis medicinally or otherwise whilst pregnant or breastfeeding.  

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