London: Smoking cannabis during pregnancy may lead to abnormal brain structure in children, a new study has warned.

Compared with unexposed children, those who were prenatally exposed to cannabis had a thicker prefrontal cortex, a region of the brain involved in complex cognition, decision-making, and working memory, the findings showed.

“This study is important because cannabis use during pregnancy is relatively common and we know very little about the potential consequences of cannabis exposure during pregnancy and brain development later in life,” said study author Hanan El Marroun from Erasmus University Medical Centre in The Netherlands.

An estimated two-thirteen per cent of women worldwide use cannabis during pregnancy. Previous studies have identified short and long-term behavioural consequences of prenatal cannabis exposure, but effects on brain morphology were unknown.

“Understanding what happens in the brain may give us insights in how children develop after being exposed to cannabis,” El Marroun said.

For the study, the researchers used structural magnetic resonance imaging to examine the brains of 54 children, six to eight years old, who were prenatally exposed to cannabis.

Most of the children exposed to cannabis were also exposed to tobacco, so the researchers compared them to 96 children prenatally exposed to tobacco only, as well as to 113 control children with no exposure.

The children were part of a prospective population-based study in The Netherlands.

Comparing tobacco-exposed children with children exposed to both tobacco and cannabis revealed differences in the cortical thickness, suggesting that cannabis exposure has different effects than tobacco.

The findings were detailed in the journal Biological Psychiatry.

“The current study combined with existing literature does support the importance of preventing smoking cannabis and cigarettes during pregnancy,” El Marroun pointed out.