• "This is the first time that continued marijuana use in pregnancy has been independently linked to pre-term birth." (Getty Images)Source: Getty Images
Around 12 per cent of pregnant women, observed at an Adelaide-based centre, used marijuana before or during their pregnancy despite the fact the drug could induce a pre-term birth and cause damage to an unborn child, a new international study shows.
Yasmin Noone

13 May 2016 - 2:19 PM  UPDATED 13 May 2016 - 2:19 PM

Pregnant women who continue to use marijuana until 20 weeks gestation are five times more likely to give birth to a premature baby than women who don’t use the drug at all, international research released this week shows.

The world-first study, led by University of Adelaide researchers, found Australian usage rates were the highest of the four developed countries evaluated (Australia, New Zealand, the UK and Ireland), with 12 per cent of pregnant women from the Adelaide-based centre using marijuana either before pregnancy, affecting egg quality, or during pregnancy, affecting the fetus directly.

This was in contrast to five per cent of pregnant women in New Zealand using marijuana before or during pregnancy, and four per cent of pregnant women from Ireland and the United Kingdom.

The results also indicate that over 8.5 per cent of Australia women stopped using the drug in the first five months of their pregnancy. However, at 20 weeks gestation, 3.3 per cent of Australian women studied were still using marijuana.

Given that over 300,000 babies are born in Australia each year, it's estimated that around 9,900 women are continually using marijuana throughout the course of their pregnancy.

“That’s a worry because that is a significant proportion of women who are at risk of having a much earlier pre-term delivery,” says lead author Professor Claire Roberts from the University's Robinson Research Institute.

“And babies who are born pre-term are more likely to die and have a significant handicap, as a consequence of being born too early.”

“That’s a worry because that is a significant proportion of women who are at risk of having a much earlier pre-term delivery.”

Professor Roberts reasons that Australia’s marijuana usage rates were so high in the study because they were linked to wealth, as most of the women involved at the Adelaide research centre were from the a low socio-economic group.

“The Adelaide cohort served to include socio-economically disadvantaged women but other centres, like the one in Auckland, focused on women who were at a socio-economic advantage.

“In disadvantaged communities, women are either not getting the message about using marijuana while pregnant or it’s not being talked about…They also do things that make them feel better and able to cope with a bad lot. Using marijuana is one of those things.”

Prof Roberts adds that pregnant women from advantaged communities might not own up to using marijuana so this group could be underrepresented in the figures.

“They may be more ashamed to say they use it but you’d have to assume affluent women are using drugs. There are just far fewer affluent women who are using compared to those from disadvantaged communities.”

“Based on our findings, we consider marijuana to be a major public health concern for pregnant women and their babies."

The study, published in Reproductive Toxicology, shows that more than six per cent of pre-term births could have been prevented if women did not use marijuana during pregnancy.

“Based on our findings, we consider marijuana to be a major public health concern for pregnant women and their babies.

“We can’t say there is a time during gestation where it’s okay to use marijuana so we say just stop. We recommend women abstain completely.”

Researchers investigated the marijuana habits of 5,500 women across four countries and found that, internationally, around 5.6 per cent of women used marijuana before or during pregnancy. An average of 4.6 per cent of women stopped using marijuana within the first five months of their pregnancy, leaving one per cent of women - equivalent to an estimated 300,000 women - still using at marijuana 20 weeks gestation.

Over 35 per cent of marijuana users gave birth at less than 28 weeks' gestation compared to five per cent of non-users.

Around 64 per cent of users delivered their babies at less than 32 weeks versus 16 per cent of non-users.

No one knows why marijuana causes damage to an unborn child but it is believed that the drug has the ability to leak into the placenta and could bind to the endorphin receptors in the brain and even cross the placental barrier.

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