Doctors have warned women not to smoke cannabis during pregnancy after a landmark study found those who do face double the average risk of going into labour prematurely.
The news comes despite a growing belief among young people that cannabis is harmless because it is ‘natural’ and may have medicinal properties.
But now Canadian researchers have found that cannabis use during pregnancy is linked to a much higher possibility of a premature birth – putting the baby at serious risk.
The study found that almost one in eight women who smoked cannabis while pregnant delivered before 37 weeks, which is classed as premature. In contrast, the chance of a premature birth for women who avoided the drug was just one in 17.
Those who used cannabis in pregnancy were also more likely to suffer a serious complication called placental abruption, during which the placenta separates from the wall of the womb. The condition can be fatal for the unborn child.
In addition, the babies of cannabis smokers were more likely to require care on a neonatal ward, according to the research, reported in the Journal of the American Medical Association.
Dr Pat O’Brien, of the Royal College of Obstetricians and Gynaecologists, said: ‘This new study adds to a growing body of evidence which shows smoking cannabis during pregnancy is associated with adverse outcomes for women and their children, including pre-term birth.
In the study, researchers examined 661,617 births between 2012 and 2017 in Ontario, where pregnant women are routinely asked about their drug use.
Among these women, 5,639 admitted using cannabis during pregnancy. Researchers found the smokers were at double the risk of having a premature birth than non-users.
The team also tried to account for the possibility that women who smoke cannabis in pregnancy might be at a higher risk of premature birth for other reasons, such as being more likely to smoke cigarettes or drink alcohol.
After performing this analysis, they still found women using cannabis in pregnancy were 41 per cent more likely to have a premature birth than women who did not.
Professor Daniel Corsi, lead author of the report, said: ‘We recommend against using cannabis in pregnancy.
‘The best advice for women would be to speak to their healthcare provider, physician or midwife to discuss alternatives to cannabis for treating morning sickness.’