Cannabis is never far from the news headlines these days, with several U.S. states and countries around the world taking steps to decriminalize the drug. In response, a wave of academic studies into the health effects of smoking weed have been published, often with wildly conflicting findings. The latest of these, which appears in the journal BMJ Open, takes a look at the consequences of using marijuana during pregnancy, producing evidence that doing so may not be such a smart move.

Researchers from the University of Arizona conducted an analysis of 24 different studies into the effects of smoking cannabis during pregnancy. In particular, they included studies that contained information about how the drug impacts on factors such as birth weight, head circumference, preterm birth and the likelihood of newborn babies being placed in intensive care. They also looked for relationships between marijuana use and maternal health, focusing on how smoking weed contributes to anemia in new mothers.

Results were somewhat murky, with several of the studies seeming to contradict each other, although a number of general patterns could be observed when looking at the data as a whole. For instance, although a small number of studies indicated that babies born to mothers who smoked cannabis were actually heavier than those whose mothers did not use the drug, the overall picture indicates that infants exposed to cannabis in the womb were 77 percent more likely to be born underweight.

Babies were also around twice as likely to end up in intensive care during the first six weeks of their life if their mothers had smoked the drug while pregnant. Additionally, although five studies found no connection between marijuana use and anemia in new mothers – a condition characterized by a deficiency of red blood cells – one study, containing a sample of 8,350 people, indicated a strong connection between the two. Considering all six of these studies together, the researchers found that using marijuana during pregnancy causes a 36 percent increase in the risk of mothers suffering from anemia in the six weeks after giving birth.

Based on these findings, the authors conclude that “as use of cannabis gains social acceptance, pregnant women and their medical providers could benefit from health education on potential adverse effects of use of cannabis during pregnancy.”

However, they are also quick to point out that “many cannabis users are often tobacco or alcohol users”. Since both alcohol and tobacco use during pregnancy have been shown to generate a range of negative health effects for newborns, including low birth weight, the study authors concede that their findings may be caused by these substances rather than cannabis.

As such, they conclude that more research is needed in order to determine how cannabis alone affects the health of new mothers and their newborn babies, urging that their findings “be interpreted with caution” until further studies are conducted.