"This recommendation is based on evidence for potential harm
including decreased birthweights of fetuses exposed to marijuana and
concern for an impact on neurological development based on
longitudinal human studies," said Dr. Torri Metz of the University
of Utah School of Medicine in Salt Lake City.
"More recent data also identifies a possible association between
marijuana use and neonatal intensive care unit admission and
stillbirth," Metz, coauthor of the evidence review of marijuana use
in pregnancy and while breastfeeding, said by email.
As more U.S. states legalize marijuana, concern is mounting in the
medical community that many people, including pregnant women, may
mistakenly assume that using the drug is risk-free, the researchers
note in Obstetrics & Gynecology.
The American College of Obstetricians and Gynecologists discourages
doctors from prescribing or suggesting the use of marijuana for
medicinal purposes while women are trying to conceive, pregnant or
nursing their babies.
"There are no studies in which women who used marijuana for a
condition are compared to those who did not in order to evaluate the
efficacy of marijuana use for treating medical conditions in
pregnancy," Metz said. "As such, we do not have any evidence of a
benefit of marijuana use in pregnancy."
Marijuana used by pregnant women can cross the placenta to reach
babies in the womb, and it can also pass into breast milk and reach
nursing babies, previous research has shown.
"Active ingredients in marijuana like THC pass through the placenta
directly exposing the fetus, which can impact the infant's overall
development, particularly brain development," said Dr. Cynthia
Rogers of Washington University School of Medicine in St. Louis.
"The brain has receptors for these active ingredients in marijuana
very early on in gestation. It is therefore possible that exposure
to marijuana during pregnancy alters fetal brain development because
these brain receptors are exposed to these ingredients at higher
levels than the developing brain is expecting," Rogers, who wasn't
involved in the evidence review, said by email.
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"What we still do not yet know from infant studies is exactly how
exposure to marijuana affects human infant brain development at
birth or throughout childhood with continued exposure either through
lactation or through second-hand smoke exposure," Rogers added.
Another limitation of research to date is that much of it has been
done in animals.
Many studies in humans, meanwhile, have relied on women to
accurately recall and candidly report on their drug use, which may
not offer a reliable picture of exactly how exposure to the drug
effects their babies.
Scientists also don't know how different types and amounts of
cannabis use might affect pregnant women and their babies.
"Much of what we know about prenatal marijuana exposure comes from
earlier studies that were conducted when marijuana was not as strong
as what is currently available, so we are probably under-estimating
the effects of prenatal marijuana use on offspring development,"
said Gale Richardson of the University of Pittsburgh School of
All of this makes it difficult for doctors to give women
evidence-based advice, particularly when it comes to one of the most
common reasons pregnant women use cannabis: nausea.
Cannabis can indeed ease nausea, but most of the research in this
area has focused on cancer patients who have nausea as a side effect
"Although many pregnant women report using recreational marijuana to
treat nausea and vomiting, marijuana use itself may cause nausea and
vomiting, especially in women who have been using it daily for a
long period of time," Richardson, who wasn't involved in the
evidence review, said by email.
SOURCE: https://bit.ly/2zYNpoI Obstetrics & Gynecology, November
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