The prevalence and significance of gestational cannabis use at an Australian tertiary hospital

Background Cannabis is one of the most common non-prescribed psychoactive substances used in pregnancy. The prevalence of gestational cannabis use is increasing. Aim The aim was to examine the prevalence of gestational cannabis use and associated pregnancy and neonate outcomes. Materials and Methods A retrospective observational study involving pregnant women delivering in 2019 was conducted at a tertiary hospital in Perth, Western Australia. Gestational cannabis and other substance use records were based on maternal self-report. Pregnancy outcomes included neonatal gestational age, birthweight, birth length, head circumference, resuscitation measures, special care nursery admission, 5-min Apgar score and initial neonatal feeding method. Results Among 3104 pregnant women (mean age: 31 years), gestational cannabis use was reported by 1.6% (n = 50). Cannabis users were younger, more likely to use other substances and experience mental illness or domestic violence compared with non-users. Neonates born to cannabis users had a lower mean gestational age, birthweight and birth length compared to those born to non-cannabis users. Gestational cannabis use (odds ratio (OR) 3.3, 95% confidence interval (CI) 1.6-6.7) and tobacco smoking (OR 2.2, 95% CI 1.5-3.6) were associated with increased odds of a low-birthweight neonate. Combined cannabis and tobacco use during pregnancy further increased the likelihood of low birthweight (LBW, adjusted OR 3.9, 95% CI 1.6-9.3). Multivariate logistic regression analysis adjusted for maternal sociodemographical characteristics, mental illness, alcohol, tobacco and other substance use demonstrated gestational cannabis use to be independently associated with LBW (OR 2.3, 95% CI 1.1-5.2). Conclusion Gestational cannabis use was independently associated with low birthweight, synergistically affected by tobacco smoking.