The association between legalization of recreational marijuana use and birth outcomes in Colorado and Washington state.

OBJECTIVE: To identify trends in birth outcomes that may be associated with legalization of recreational marijuana which occurred in 2013 using vital records from Colorado and Washington states for the period of 2008-2016. METHODS: Data were from birth certificates of live births (between 22 and 44 weeks gestation) of which there were 576,369 singleton births included for Colorado and 771,547 for Washington State. Outcomes included preterm birth defined as <37 completed weeks of gestation; small for gestational age (SGA) defined using <10th percentile birthweight z-score; and birth prevalence of congenital anomalies defined using a variable from the birth certificate that indicated any major defect. The outcomes of interest were analyzed using a change-point approach to logistic regression adjusting for maternal socio-demographics, body mass index, smoking, and infant sex. RESULTS: There was evidence of an increased birth prevalence of congenital anomalies in both Colorado and Washington State when comparing prevalence before and after legalization. Only in Colorado did we observe an increase in preterm births post legalization, and there was no association with fetal growth in either state. CONCLUSION: This time trend analysis indicates that the birth prevalence of all congenital anomalies combined in Washington and Colorado has increased in parallel with the timing of legalization of marijuana in those two states. However, this finding can only generate hypotheses as no pregnancy exposure information for marijuana was available in this dataset. More research is needed on the effect of marijuana use on birth outcomes.