Marijuana is often used during pregnancy, but it can get the child off to a lower-than-average start on development and health

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Users and sellers of marijuana may suggest that expectant mothers use it to alleviate side effects of pregnancy, especially morning sickness, and research has found that it is the drug most commonly used during pregnancy. But other research increasingly shows "adverse outcomes for children when cannabinoids are consumed during pregnancy," says a study published in Frontiers in Pediatrics.

"Even with marijuana use limited to the first trimester of pregnancy, we demonstrate a noteworthy average reduction in birth weight of over 150 grams," more than 5 ounces, said Dr. Beth Bailey, director of population health research at Central Michigan University and senior author of the study. "Furthermore, if marijuana use persisted into the second trimester, a significant decrease in newborn head circumference was observed."

That matters, said Dr. Phoebe Dodge, the study's first author: "Newborn size serves as a robust indicator of future child health and development."

Other studies "have provided compelling evidence regarding the substantial impact of cannabis use on newborn size," the journal reports. "The most pronounced deficits in size were observed among infants exposed to marijuana throughout the entire gestational period," Bailey said. "Infants exposed to cannabis throughout pregnancy exhibited a reduction in birth weight of approximately 200 grams and a decrease in head circumference of nearly 1 centimeter," just under 0.4 inch.

"The research revealed that even occasional use, such as for managing first-trimester morning sickness, can lead to reduced fetal growth similar to the effects seen with continued cannabis use throughout pregnancy," the journal reports. 

That said, the study authors didn't know just how much or how often the participants used marijuana, just whether or not they did at all So, they could not "establish a direct correlation between heavy cannabis use and more pronounced outcomes in newborn growth," the journal reported.

But Dodge emphasized, "The best course of action is for women to be advised to cease marijuana use prior to conception." If you're already become pregnant, "The second-best option is to quit as soon as possible in order to mitigate potential long-term adverse health and developmental consequences."

The Centers for Disease Control and Prevention has more information.