AWomen using marijuana while pregnant have a five times higher risk of spontaneous pre-term birth, new research shows.
Screening for Pregnancy Endpoints (SCOPE) investigators interviewed 5588 women as a means to develop screening tests to predict small-for-gestational-age neonates, pre-eclampsia, and spontaneous pre-term birth.
The women were interviewed at around 15 to 20 weeks of pregnancy.
Researchers found the small sample of women who used cannabis were at an increasingly higher risk of spontaneous pre-term birth regardless of socio-economic status and whether they smoked tobacco.
"In this large group, maternal marijuana use was a major contribution to the risk of early birth and was consistent for cigarette smokers and non-smokers," lead author professor Lesley McCowan said.
"Of particular concern was that women who continued to use marijuana had a higher risk of delivering very pre-term when the risks of long term consequences for the baby are greatest."
Around one in 20 women surveyed reported using cannabis before or during the first half of their pregnancy.
"In the group of women that we looked at, we estimate a 6.2 percent reduction in the incidence of spontaneous pre-term birth is possible, if women are not exposed to marijuana during early pregnancy."