Study Links Marijuana Use During Pregnancy To Smaller Babies

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Blonde girl holding red joint

Smoking during pregnancy has been taboo for at least a generation or two now, but with more and more states legalizing marijuana researchers are finding it too can negatively impact a baby’s health.

Researchers from the University of Buffalo Research Institute on Addiction found that prenatal marijuana use can have consequences for a baby’s size and can influence behavior issues, especially if coupled with tobacco.

Marijuana Use During Pregnancy - The Everyday Mom Life

Published in the March/April issue of Child Development, the study looked at 250 infants and their mothers. In 173 of the cases the infants had been exposed to tobacco and/or marijuana during pregnancy. None were exposed to substantial amounts of alcohol.

“Nearly 30 percent of women who smoke cigarettes during pregnancy also report using marijuana,” says Rina Das Eiden, PhD, RIA senior research scientist in an interview with Science Daily. “That number is likely to increase with many states moving toward marijuana legalization, so it’s imperative we know what effects prenatal marijuana use may have on infants.”

Elden found that infants who had been exposed to both tobacco and marijuana were smaller in length, weight and head size.

In fact, babies exposed to marijuana were also more likely to be smaller when compared to babies only exposed to tobacco products. This was especially true of babies who were exposed during the third trimester and was more pronounced in boys versus girls.

Babies exposed to marijuana were also more likely to be born earlier than babies who were not exposed to anything.

“We also found that lower birth weight and size predicted a baby’s behavior in later infancy,” Eiden said in an interview with Science Daily. “Babies who were smaller were reported by their mothers to be more irritable, more easily frustrated and had greater difficulty calming themselves when frustrated. Thus, there was an indirect association between co-exposure to tobacco and marijuana and infant behavior via poor growth at delivery.”

Additionally, women who were more stressed throughout pregnancy – showing signs of anger, hostility and aggression – were more likely to continue to use marijuana and tobacco for the duration. The babies’ irritability and frustration are also linked to mother’s who reported higher levels of stress.

“Our results suggest that interventions with women who smoke cigarettes or use marijuana while pregnant should also focus on reducing stress and helping them cope with negative emotions,” Eiden said in an interview with Science Daily. “This may help reduce prenatal substance exposure and subsequent behavior problems in infants.”

You can find the abstract and read more about the study here. For more news from The Everyday Mom Life, click here.


  1. I read this study when I was pregnant. I would get so mad when people would post on the what to expect Message boards that they were smoking weed while pregnant.

  2. OMG, why would anyone need a study to know that you shouldn’t put anything into your body when you’re pregnant?! I mean, I gave up caffeine when I was pregnant! Smoking pot? Come on. That’s just stupid.

  3. Not surprising that there are adverse side effects. It’s good to have these statistics for people to see and do things to care for themselves and their baby during pregnancy.

  4. This makes me so sad, why would a mom put their baby at risk like this. I remember being worried about the wine I drank a week before we found out I was pregnant, I can’t imagine putting my baby at risk throughout my pregnancy!

  5. My mom has been a special education teacher for many years. I have seen first-hand what fetal-alcohol syndrome does to a child. I can’t imagine putting your child through that when they have no choice in the matter.

  6. I do believe anything we ingest can affect our babies. I was so scared to even drink coffee while pregnant.

  7. No one should smoke anything while pregnant. I am all for the medicinal ways marijuana can help people but while pregnant everyone needs to be clean as can be. We use enough harsh chemicals in our homes to clean not to mention the stuff put into our food.

  8. Though pregnant folks have so much information coming their way throughout the process, it’s always so important to be on top of the newest research. Thanks for putting this study out there- I’m sure it will be helpful to many.

  9. Smoking is bad for health, what more if a smoker is pregnant? Ugh. I really hope women are considerate enough when they know they have a baby inside.

  10. I’m a non smoker, and both of my kids full term were only 6lbs.. I could only imagine being a smoker, them being smaller. This is a great study. Thank you for sharign

  11. Thank for posting the study. Although I’m not a mom yet but this helps me a lot with knowledge about tobacco and marijuana. How bad are the impacts of them on innocent children!

  12. Thanks for sharing. It is important to educate people! This is a very hot topic since mothers who do smoke say it is because it helps with their morning sickness but are forgetting the effect is it having on their unborn child.

  13. I honestly get so upset and judgemental when I find out that people are smoking and drinking during pregnancy. In my opinion, wait the 9 months and then resume whatever you were doing.

  14. inhaling anything smoke related into your lungs has an effect on a fetus/baby… I find it kind of shocking and selfish for mothers to smoke, do drugs, and drink alcohol while pregnant… And there after for both parents to expose their babies/kids to 2nd hand smoke, esp since it affects their young ones health (not just the parents!)

  15. This is very interesting study. I’d never guess that. I love to read studies like these. I don’t smoke anything it is good to be aware.

  16. I knew it! Smoking is never good for the body. How much more if you are pregnant? But the fact that it’s legal makes anyone think that it’s good. Coz if it’s bad, why would it be legalized in the first place? Thanks for laying out this information in the open.

  17. It is hard to think anyone would encourage smoking of any kind during pregnancy. Even daily medications can be detrimental! Hopefully this will open someone’s eyes


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