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Cannabis use in pregnancy linked to low birthweight

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Use of cannabis during pregnancy is linked to low birthweight and the subsequent need for intensive care, according to US researchers.

They cautioned that, as cannabis became more socially acceptable, it was important that prospective mothers and clinicians were fully informed on the potential harms of using the drug during pregnancy.

“There does appear to be negative consequences associated with in utero exposure to cannabis”

Study authors

They noted that, while previous research had focused on the drug and potential links to respiratory and mental illness, less was known about its possible effects on foetal growth and development.

The researchers trawled seven research databases for studies published up to 2014, looking at the effects of cannabis use during pregnancy on mother and baby up to six weeks after the birth.

Outcomes, such as anaemia in the mother, birthweight, baby’s length, need for neonatal intensive care, head circumference and early birth were all included in the review of 24 studies.

Analysis of the data showed that mothers-to-be who used cannabis were 36% more likely to have anaemia than women who did not use the drug.

Infants exposed to cannabis in the womb were 77% more likely to be underweight at birth and twice as likely to require intensive care as those whose who had not used cannabis during pregnancy.

The researchers acknowledged they were unable to extract data on whether any of the study participants used other illicit drugs or how much alcohol they drank – factors known to be associated with a higher risk of low birthweight and premature birth.

However, they stated: “There does appear to be negative consequences associated with in utero exposure to cannabis, including a decrease in birthweight and a need for placement in [intensive care].”

As medical and social use of the drug “is rapidly becoming more acceptable”, understanding its effects on maternal and foetal health “should become a global priority,” they said in the journal BMJ Open.

Women and their clinicians could do with more information on the possible harms of using the drug during pregnancy, they added.

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Readers' comments (1)

  • Let's hope that nurses have the ability to read this research with a critical eye.

    This study is purely data collection, based on databases and other studies. While a good, wide source of data has been used, it states quite accurately in the limitations of the study, "Many cannabis users are often tobacco or alcohol users; hence, determining a cannabis-only effect (excluding the presence of tobacco and alcohol) was currently not possible, as most studies did not exclude participants with polysubstance use." when we know quite categorically that both tobacco and alcohol have been proven to give the issues in this study. It cannot state ''cannabis causes 'x''' it can merely point to issues that require further, accurate study. Smoking cannabis with tobacco has always been a health risk but is often the only way people know or find effective. A study showing the use of medibles during pregnancy may have a different outcome.

    Also, cannabis has been shown to have absolutely remarkable properties for treating hyperemesis gravidarum. Inability to hold down food or absorb nutrition is far more risky.

    Links to evidence/studies here:

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