Relationship between mandatory warning signs for cannabis use during pregnancy policies and birth outcomes in the Western United States

As U.S. states legalize recreational cannabis, some enact policies requiring Mandatory Warning Signs for cannabis during pregnancy (MWS-cannabis). While previous research has found MWS for alcohol during preg-nancy (MWS-alcohol) associated with increases in adverse birth outcomes, research has not examined effects of MWS-cannabis. This study uses Vital Statistics birth certificate data from June 2015 - June 2017 in seven western states and policy data from NIAAA's Alcohol Policy Information System and takes advantage of the quasi -experiment created by Washington State's enactment of MWS-cannabis in June 2016, while nearby states did not. Outcomes are birthweight, low birthweight, gestation, and preterm birth. Analyses use a Difference-in -Difference approach and compare changes in outcomes in Washington to nearby states in the process of legal-izing recreational cannabis (Alaska, California, Nevada) and, as a secondary analysis, nearby states continuing to criminalize recreational cannabis (Idaho, Montana, Wyoming). Birthweight was-7.03 g lower (95% CI-10.06,-4.00) and low birthweight 0.3% higher (95% CI 0.0, 0.6) when pregnant people were exposed to MWS-cannabis than when pregnant people were not exposed to MWS-cannabis, both statistically significant (p = 0.005 and p = 0.041). Patterns for gestation,-0.014 weeks earlier (95% CI-0.038, 0.010) and preterm birth 0.2% higher (95% CI-0.2, 0.7), were similar, although not statistically significant (p = 0.168 and 0.202). The direction of findings was similar in secondary analyses, although statistical significance varied. Similar to MWS-alcohol, enacting MWS-cannabis is associated with an increase in adverse birth outcomes. The idea that MWS-cannabis provide a public health benefit is not evidence-based.