Mothers who smoke marijuana while pregnant double the possibility of giving birth to a premature baby. That’s according to an international study led by the University of Adelaide researchers.

Babies who are born at least three weeks before their due date can face serious complications and life-threatening health problems, some of which only show up later in life, such as heart disease and diabetes.

Risks of a premature birth

A recent study analysing over 3000 pregnant women in Adelaide, Australia and Auckland in New Zealand, has detailed the most common risk factors for preterm babies. The results were recently published in the Journal PLoS ONE.

The research team, led by Professor Gus Dekker from the University of Adelaide's Robinson Institute and the Lyell McEwin Hospital, found that the greatest risks for spontaneous preterm birth included:

• Strong family history of low birth weight babies (almost six times the risk);
• Use of marijuana prior to pregnancy (more than double the risk);
• Having a mother with a history of pre-eclampsia (more than double the risk);
• Having a history of vaginal bleeds (more than double the risk);
• Having a mother with diabetes type 1 or 2 (more than double the risk).

The team also found that the greatest risk factors leading to a premature birth included:

• Mild hypertension not requiring treatment (almost 10 times the risk);
• Family history of recurrent gestational diabetes (eight times the risk);
• Receiving some forms of hormonal fertility treatment (almost four times the risk);
• Having a body mass index of less than 20 (more than double the risk).

Smoking and drinking while pregnant

Regardless of public health campaigns, several women continue to use substances such as tobacco, marijuana and alcohol during pregnancy – and their usage rebounds to pre-pregnancy levels within two years of having a baby – that’s according to a University of Washington study.

Men’s patterns of substance use during their partners’ pregnancies was shown to stay the same. Since men are generally left off the hook by these campaigns, their levels of binge drinking, daily smoking and marijuana use remained fairly stable before, during and after pregnancy – the study showed.

According to the study’s lead authors Jennifer Bailey and Karl Hill, this finding is important because men’s substance use may make it more difficult for women to stop while they’re pregnant.

"The months after childbirth are critical for intervening with mothers," said Bailey, who is a UW research scientist. "For example, many already have done the hard work of quitting smoking and haven't smoked a cigarette in six months or more. We should support that effort so that they can continue as non-smokers. However, we know if dad is smoking or drinking it is more likely that mom will resume smoking or drinking."