Study Finds Link Between Marijuana Use During Pregnancy and Low Birth Weight

Marijuana use throughout pregnancy increased the risk of adverse health problems for the newborn, but not for expecting mothers who only used it during the first trimester.

New research suggests there is a link between marijuana use during pregnancy and an increased risk of giving birth to infants who are stillborn or suffer from health side effects, such as low birth weight.

The findings were published this week in the Journal of the American Medical Association (JAMA), indicating that pregnant women who use marijuana may be 26% more likely to give birth to a child with health complications than their peers.

Researchers from the University of Utah Health conducted a study including data for nearly 10,000 patients across eight U.S. medical centers. They used frozen urine samples stored from three points during pregnancy as part of the Nulliparous Pregnancy Outcome Study: Monitoring Mothers-to-Be.

Expecting mothers were recruited from 2010 through 2013, and samples were taken during visits occurring during pregnancy weeks 6 to 13, between weeks 16 to 21, and between weeks 22 and 29. The samples were analyzed for tetrahydrocannabinol (THC), more commonly known as marijuana.

Researchers divided the women’s marijuana use into those who used during the first trimester only, those who used it throughout pregnancy, and women who did not use marijuana at any time during their pregnancy.

Overall, 7%, or roughly 610 patients, used weed during pregnancy. Of that group, only about a third used marijuana just during their first trimester. However, more than two-thirds of the women who used marijuana did so throughout their pregnancy.

Pregnancy Marijuana Use Linked to Low Birth Weight

According to the findings, women who used marijuana throughout their pregnancy had a 26% increased risk of giving birth to an infant who suffered health complications. Infants born to mothers who used marijuana during pregnancy were 50% more likely to have a low birth weight.

Low birth weight can be serious for infants. Infants with low birth weight are often 95% smaller than other infants. And low birth weight increases their risk of suffering other health side effects such as fighting infections, gaining weight, and staying warm.

Infants born to mothers who used cannabis were also more likely to be stillborn, require neonatal intensive care admission (NICU), suffer from hypertension, and suffer other complications or death, the researchers concluded, indicating that marijuana exposure appears to be linked to placental dysfunction.

Even after researchers adjusted for other factors like medical conditions, nicotine use, and socioeconomic factors, the increased risk was still relevant, they determined.

However, the researchers found that the infants of those women who limited their cannabis use to only the first trimester appeared to face no increased risk of health complications or death. The researchers indicated that more studies need to be done to determine the full health effects and potential risks.

Marijuana Use Pregnancy Concerns

As more states in the U.S. legalize the use of marijuana, cannabis use continues to increase among reproductive-age individuals. Many dispensaries recommend marijuana use to help with nausea and morning sickness, despite little data existing to advocate for its safe use during pregnancy.

A study published in 2022 indicated pot use during pregnancy can increase the risk the child will suffer from aggressive behavior, conduct disorders, and attention deficit hyperactivity disorder (ADHD).

Other research has linked marijuana use during pregnancy to increased risk of pre-term birth, as well as behavioral and mental health issues later in childhood.

“In this multicenter cohort, maternal cannabis use ascertained by biological sampling was associated with adverse pregnancy outcomes related to placental dysfunction,” researchers in this latest study determined. “Cannabis use should be avoided during pregnancy to optimize maternal and neonatal outcomes.”