Over 3000 Australian and New Zealand women were involved in the study, which looked at factors that can influence preterm birth. When they tabulated all the data, smoking marijuana pre-pregnancy appeared to double the odds of preterm birth.
But how much pot? A puff once in high school? A daily habit for ten years? A daily habit, ten years ago?
Looking at the actual study, I can’t see any quantities specified (which is disappointing). This is what it says though:
“We have shown that marijuana is a strong environmental risk factor for [preterm birth] in this population. We are unable to determine whether this association is due to a toxic effect of marijuana or is a marker of a suite of lifestyle factors that contribute to the risk. Pre-pregnancy marijuana use may be a more reliable marker since one can anticipate that women would be more likely to disclose it than persistent marijuana use during pregnancy. In contrast to the results of this large prospective cohort study, large American population studies did not find an association between maternal marijuana use and preterm birth.” (my italics)
So … they don’t really know if it’s pot smoking before pregnancy or related lifestyle factors or even if this group only smoked pot before pregnancy and not during. Hmm.
I’ve researched pot smoking during pregnancy before and found that while obviously bound to be controversial and defiant of the standard recommendation to “avoid street drugs during pregnancy,” the question of how harmful it can be is not easy to answer. As the above quote suggests, it’s hard to get good information (people can lie, this drug is still illegal in many places) and pot smokers are more likely to do other things that could lead to preterm birth such as smoking cigarettes or taking other drugs. We do know that pot stays in your system for a long time and that drugs pass through the placenta, so the drug is likely getting to the baby. But we don’t know exactly what it does when it gets there.
This study also found some less scandalous but perhaps more intriguing connections. The strongest risk factor for preterm birth was a strong family history of low birthweight babies. Other risks include a history of pre-eclampsia, vaginal bleeds, and diabetes. Preterm rupture of the membranes (PROM) was also associated with mild hypertension (10 times increased risk), family history of gestational diabetes, hormonal fertility treatment (four times the risk) and a body mass index under 20 (double the risk).
The authors of the study don’t make a large fuss about the pot smoking (though I’m sure others will) but rather note in a press release that “the risk factors for … preterm birth vary greatly, with a wide variety of health conditions and histories impacting preterm birth.”
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