Cannabis use during pregnancy is harmful to the development of the fetus, which has a higher risk of being born with low weight, which can have consequences for its long-term health, according to research that has analyzed data from 9,257 pregnant women of USA. Cannabis, researchers argue, affects the function of the placenta and reduces the transfer of oxygen and other nutrients from the mother to the fetus.
“Cannabis consumption in pregnant people has increased in the last decade in parallel with a growing perception of its safety,” the authors of the research write in the journal JAMA, where they present their results today. But they point out that most studies on cannabis and pregnancy have evaluated consumption based on surveys, which are unreliable, and have not taken into account variables that could bias the results, such as associated tobacco consumption.
To overcome these problems, the new research has been based on data from the Nulliparous Pregnancy Outcomes Study, in which some 10,000 volunteers provided urine samples throughout their pregnancy. In this way, it has been possible to quantify exposure to cannabis, tobacco and other substances by analyzing the metabolites that pass into the urine.
The researchers, led by Torri Metz, from the University of Utah, have analyzed data from 9,257 women, of whom 610 were exposed to cannabis during the first trimester of pregnancy. Of them, 413 maintained exposure to cannabis until the third quarter.
8.6% of pregnant women exposed to cannabis had a child of low weight for their gestational age. After assessing variables such as smoking, obesity, other diseases and sociodemographic characteristics, the researchers conclude that the risk of having a low-weight child is 52% higher in women who have used cannabis during pregnancy. Previous studies have shown that having a low birth weight affects neurodevelopment in childhood and increases cardiovascular risk in adulthood.
“Tetrahydrocannabinol [or THC, the main active component of cannabis] is neurotoxic for the developing brain,” says Eduard Gratacós, specialist in fetal medicine and director of BCNatal, a center attached to the Clínic and Sant Joan de Déu hospitals, which has not participated in the research. Gratacós points out that “perhaps there is not as much awareness about the effects of cannabis [on the fetus] as there is about those of tobacco and alcohol.”
In Spain, 10% of pregnant women are exposed to cannabis at the beginning of pregnancy, according to a study by the Spanish Association of Pediatrics (AEP) presented in 2019. Four out of ten cases were due to active consumption by the pregnant woman and the other six for passive consumption. The AEP also warns that THC accumulates in breast milk, where the concentration is eight times higher than in the blood, which is why it advises against the use of cannabis during breastfeeding.
New research from the US suggests that the risk of stillbirth, premature birth and admission of the newborn to the neonatal intensive care unit are higher in women who use cannabis during pregnancy. But since these are relatively infrequent problems, not enough cases have been recorded for the results to be statistically significant.
To gain statistical power, the researchers have jointly analyzed all the adverse outcomes of the pregnancies studied. The result indicates that the risk of having any of these problems (which include gestational hypertension, placental abruption, low birth weight, premature birth, cesarean section, stillbirth and neonatal death, among others) is 27% higher in exposed women to cannabis.
The risk is greater in women who consume cannabis throughout pregnancy than in those who do so only during the first trimester, and greater the higher the dose consumed. But even in women who have only been exposed to cannabis during the first trimester, there is an 18% increased risk of suffering a serious complication.
“It is a very well done study that confirms the results of previous studies” on the harmful effects of cannabis during pregnancy, assesses Eduard Gratacós, from BCNatal. "The majority of cases of consumption of these substances are not reported to health professionals, so the perception that doctors have about their consumption is lower than reality." For this reason, Gratacós reminds us of the importance of asking and informing about the use of cannabis and other substances during the medical monitoring of pregnancy.
