Research identifies vascular effects of marijuana consumption during pregnancy

Understanding the changes that the fetus undergoes when exposed to cannabis will help to improve the prevention of consumption and the monitoring of pregnant cannabis users.


A study conducted in the Perinatal Psychiatry Program of Vall d'Hebron has determined the vascular effects of marijuana use during pregnancy. This program focused on women's mental health during pregnancy and postpartum is formed by the research groups of the Vall d'Hebron Research Institute (VHIR): Maternal and Fetal Medicine; and Psychiatry, Mental Health and Addictions. Until now it was known that cannabis consumption meant an increased risk of pregnancy complications and impaired fetal development, but the mechanisms that caused this damage were unknown. The new study published in the Acta Obstetricia et Gynecologica Scandinavica clarifies this problem by examining how exposure to Δ9-tetrahydrocannabinol (THC), the main active ingredient of this drug, affects the placental blood flow.

A total of 60 female users who continued to use cannabis, verified by urine analysis, during their entire pregnancy were monitored. In order to isolate the specific effects of marijuana, the study excluded users of multiple drugs (including alcohol). The only exception was nicotine since most users co-consume cannabis with tobacco. In order to differentiate the effects of one from the other, a control group of nicotine-only smokers was created. These two groups were counterbalanced by a control group that did not consume any toxic substance.

The study showed that cannabis users experienced placental and fetal pulsatility changes that became noticeable in the third trimester. Some of these were shared with tobacco smokers and others were unique. 

The shared effects were: antagonistic alterations in the blood flow of the umbilical and middle cerebral arteries - the circulation of the umbilical artery accelerated, while the middle cerebral artery slowed down.

The repercussions that are considered unique to cannabis were: an increase in uterine artery flow and alterations in the cerebral placental ratio. The latter indicate modifications to blood circulation between the heart and the brain and may be linked to diseases such as intrauterine growth retardation and other complications. Still, more research is needed to isolate the effects of the two drugs fully and to rule out interference with the outcomes of other risky behaviors that are very common in frequent marijuana users.

In the future, the research team hopes that the results of this study will help to reduce the complications derived from cannabis consumption during pregnancy, improve the prevention and detection of consumption, as well as promoting a healthy lifestyle during pregnancy away from the consumption of intoxicants.

The study showed that cannabis users experienced placental and fetal pulsatility changes that became noticeable in the third trimester.

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