This supplemental material provides additional information about the study on prenatal cannabis use and maternal pregnancy outcomes. The study used data from the Kaiser Permanente Northern California (KPNC) health system. Prenatal substance use was assessed through urine toxicology tests conducted during the first prenatal visit, typically at 8-10 weeks gestation. The study included a comprehensive set of screening methods and diagnostic criteria for identifying maternal health outcomes during pregnancy, including ICD-9/10 diagnosis codes and other criteria. The study analyzed the socio-demographic characteristics of pregnancies included and excluded due to missing data on prenatal cannabis use. It also examined pregnancy characteristics and maternal outcomes based on the frequency of prenatal cannabis use. Risk ratios for maternal outcomes associated with any prenatal cannabis use were calculated, adjusting for various factors such as sociodemographic characteristics, parity, birth year, prenatal care initiation, pre-pregnancy BMI, and non-cannabis substance use. Sensitivity analyses were conducted to assess the robustness of the findings. The study found statistically significant associations between prenatal cannabis use and increased risks of certain maternal outcomes, including preterm birth, low birth weight, and placenta accreta. The results were adjusted for various confounding factors, including chronic hypertension, pre-gestational diabetes, and other medical and mental health conditions. The study highlights the importance of considering prenatal cannabis use in maternal health outcomes and underscores the need for further research to understand its long-term effects.This supplemental material provides additional information about the study on prenatal cannabis use and maternal pregnancy outcomes. The study used data from the Kaiser Permanente Northern California (KPNC) health system. Prenatal substance use was assessed through urine toxicology tests conducted during the first prenatal visit, typically at 8-10 weeks gestation. The study included a comprehensive set of screening methods and diagnostic criteria for identifying maternal health outcomes during pregnancy, including ICD-9/10 diagnosis codes and other criteria. The study analyzed the socio-demographic characteristics of pregnancies included and excluded due to missing data on prenatal cannabis use. It also examined pregnancy characteristics and maternal outcomes based on the frequency of prenatal cannabis use. Risk ratios for maternal outcomes associated with any prenatal cannabis use were calculated, adjusting for various factors such as sociodemographic characteristics, parity, birth year, prenatal care initiation, pre-pregnancy BMI, and non-cannabis substance use. Sensitivity analyses were conducted to assess the robustness of the findings. The study found statistically significant associations between prenatal cannabis use and increased risks of certain maternal outcomes, including preterm birth, low birth weight, and placenta accreta. The results were adjusted for various confounding factors, including chronic hypertension, pre-gestational diabetes, and other medical and mental health conditions. The study highlights the importance of considering prenatal cannabis use in maternal health outcomes and underscores the need for further research to understand its long-term effects.