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New research shows link between prenatal cannabis and cigarette use and low birth weight

New research from Berkeley Public Health alumna Victoria Nguyen and Professor Kim Harley shows that prenatal cannabis use is positively associated with low birth weight, with heavy users being twice as likely to give birth to a baby that is low birth weight or small for gestational age. The research, published in The Journal of Pediatrics in September, also indicated that for those who combined cannabis and cigarette use, the odds for both low weight and small for age were even higher.

While a number of studies have explored cannabis use during pregnancy, results related to infant birth outcomes are often conflicting and  epidemiologic studies done from the 1980s to the 2000s did not generally assess concomitant cigarette use. This new research, which analyzed a nationally representative cohort of data from 2017 through 2019 spanning 20 US states and territories, updates the body of literature and examines the independent and co-exposure risks of cannabis and tobacco during pregnancy.

Nguyen and Harley looked at three potential birth outcomes: low birth weight, small for gestational age, and preterm birth. They found that women who consumed both cannabis and tobacco had the greatest chances of having a low birthweight infant. Mothers with a heavy consumption of cannabis only (weekly or more frequently) were twice as likely as non-users to deliver a low birth weight infant or an infant small for its gestational age.

Additionally, the researchers found there was a higher incidence of cannabis use among those who were pregnant and do not have access to health care, an issue that historically affects more BIPOC women. Of the women sampled, 7.1% of those who are uninsured and 8.2% of those who receive public insurance reported cannabis use. This means that 92.9% of those uninsured and 91.8% of those with public insurance did not use cannabis; however, significantly more of the individuals in these groups reported cannabis use than those with private insurance (2.4%).

“We hope to shed light on marginalized populations of women who are uninsured or who lack prenatal care, since messaging on the effects of cannabis may not be known or shared with these groups,” said Nguyen.

The women believe their research could assist in removing mandatory reporting laws for those who may disclose cannabis use to their doctors.

In many cases, Nguyen said, the fear of punishment for cannabis use can lead to mistrust, avoidance of prenatal care, and worse health outcomes for both parent and infant.

“Mandatory reporting policies have actually been shown to be ineffective and even harmful to the health of both the parent and the child,” she said, indicating that such policies could actually increase the risk of infant low birthweight or preterm birth.

Harley hopes the research will be a catalyst for other studies on cannabis and birth outcomes that can evaluate cannabis dosage/potency and use during the first or second trimester of pregnancy. Many pregnant women may be using cannabis to counter morning sickness and nausea.