Cannabis use among expectant mums compromises pregnancy

Pregnant women may do well to avoid cannabis, with cannabis use in early pregnancy leading to adverse pregnancy outcomes, as reported in a study presented at Society for Maternal-Fetal Medicine (SMFM) 43rd Annual Pregnancy Meeting.

“We wanted to look specifically at cannabis use early in pregnancy because that’s when the placenta is forming, and a lot of information we currently have indicates that cannabis use does affect the placenta,” according to Dr Torri Metz, the study’s lead author and a maternal-foetal medicine subspecialist and associate professor of obstetrics and gynaecology at the University of Utah Health in Salt Lake City, Utah, US.

Metz and her team looked at 9,257 women participating in the Monitoring Nulliparous Mothers-To-Be study to examine the relationship between early pregnancy use and placentally mediated adverse pregnancy outcomes. The team analysed urine samples taken at the initial study visit (6–14 weeks’ gestation) for the presence of 11-nor-9-carboxy-delta-9-tetrahydrocannabinol (THC-COOH).

Samples from 540 participants (5.8 percent) tested positive for THC-COOH (15 ng/mL). This group of women more often experienced the composite endpoint of small for gestational age, medically indicated preterm birth, stillbirth, or hypertensive disorders of pregnancy as compared with the group of unexposed women (27.4 percent vs 18.1 percent; p<0.001). [SMFM 2023, abstract 3]

On propensity weight analyses, cannabis exposure was associated with an increased risk of the composite endpoint, Metz said. The association persisted despite adjustments for potential confounding factors such as demographics, tobacco and other drug use, medical comorbidities, and psychosocial stress.

The present data echo the findings of several studies suggesting that cannabis during pregnancy is a risk factor for poorer birth or neonatal outcomes. [Med J Aust 2020;212:519-524; BMC Pregnancy Childbirth 2020;20:771; Eur Addict Res 2021;27:131-141]

Placenta plays a crucial role during pregnancy, Metz pointed out. For the most part, the organ helps keep the baby alive and healthy in the mother’s womb by supplying oxygen and adequate nutrition, as well as removing harmful waste and carbon dioxide.  

Given that the endocannabinoid system regulates placental implantation, exogenous cannabis may thus interfere with this process, Metz said.

“With recreational marijuana use becoming legal in more states [in the US], we need better data because patients are interested in understanding the risk of cannabis use in pregnancy so they can make an informed decision,” she added.

Current data indicate that cannabis use has become widespread among pregnant women, increasing from an estimated 3.4 percent in 2002 to 7.0 percent in 2017 in the US. [JAMA 2021;326:1745-1747]

The next step in the research, according to Metz and colleagues, is to study the effect of ongoing cannabis use during pregnancy and whether “the window of exposure” matters.