A new study suggests that females and males who were frequent users of cannabis while teenagers are more likely to became parents to children born preterm and underweight.
The research, published in Scientific Reports, was a collaboration between the University of Bristol, in the UK, and Murdoch Children's Research Institute in Parkville, Australia.
The prospective study involved an Australian cohort of 665 individuals who were recruited to the study when they were in high school and followed up regularly until they started having children in their late 20s and 30s. It is the first study to explore associations between pre-conception substance use and future birth outcomes.
The results revealed that 20 percent of all preterm births in the study occurred in parents who had used cannabis daily during their teenage years.
Of the offspring whose parents reported daily cannabis use at age 15–17, a quarter were born either preterm birth or low birth weight — a frequency six times higher than in those who did not use cannabis.
Research already indicates that cannabis use by pregnant women can result in a smaller baby, but this new study suggests there could be residual effects from cannabis use twenty or more years earlier.
This investigation was unusual in including both mothers and fathers of the babies. As the researchers write in their discussion, this is worthy of note, as men are largely left out of health messaging regarding substance use and birth outcomes, which usually focuses only on antenatal tobacco and alcohol use in women.
Dr Lindsey Hines, corresponding author at the University of Bristol, said that the findings provide “additional motivation” for making sure that cannabis legalisation policies don’t inadvertently encourage use of the drug too early in life.
“There is already evidence that frequent adolescent cannabis use increases the risks for poor mental health, but our results indicate there may be further effects that individuals may not anticipate,” she said.
However, the effect on offspring was limited to those who had only used cannabis at the highest level — i.e., daily for a period between the ages of 15 and 17. Those who only used cannabis occasionally were not significantly more likely to have a preterm or low birth weight child.