Introduction: Canada has one of the highest cannabis consumption rates in the world, and given that cannabinoids readily cross the placental barrier, there exists a critical need to understand the effects of cannabis on fetal development. This study had two objectives: to determine 1) the factors associated with prenatal cannabis use, and 2) whether self-reported cannabis use is associated with the following outcomes: low birth weight, preterm birth, or small size for gestational age (GA) infants.
Methods: Maternal lifestyle questionnaire data and infant clinical data was gathered from 2229 participants in the Ontario Birth Study between 2013-2019. Women were asked about their cannabis use within three months of finding out they were pregnant, as well as during pregnancy. Multivariable linear and logistic regression was used to estimate factors associated with maternal cannabis use and to determine the association between use and selected birth outcomes.
Results: Cannabis use has increased among OBS participants since 2013. Women who use cannabis prior to finding out they were pregnant (N=216) were younger, of lower socioeconomic status, and more likely to use alcohol, tobacco, and prescription pain medication. The infants of these women were, on average, 86.8 grams lighter (95%CI: -155.3, -18.2), and had 2 times the odds of being small for GA (95%CI: 1.2, 3.3).
Conclusion: The homogeneity of the study population combined with detailed covariate measures allowed for better isolation of the effects of cannabis use (in the weeks leading up to pregnancy) on birth outcomes. An association was found, suggesting early pregnancy may be a crucial window of fetal cannabis exposure. Seeing as the birth outcomes measured in this study are intermediate outcomes that implicate adverse health outcomes later in life, prenatal care guidelines should emphasize the potential for adverse birth outcomes.