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

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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 pregnancy (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 legalizing 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.