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The association between the legalization of recreational marijuana and both small for gestational age births and NICU admissions in Colorado



To determine the association between recreational marijuana legalization and both small for gestational age (SGA) births and neonatal ICU (NICU) admissions in Colorado.

Study Design

Using interrupted time series analysis, we compared the incidence of SGA births and NICU admissions pre-/post-recreational marijuana legalization. Secondary analysis adjusted for marijuana outlet density (MOD) in maternal county of residence.


We analyzed 269,922 mother–infant dyads. SGA birth risk dropped 7% immediately post-legalization (p= 0.04), but there was no slope difference between cohorts. SGA birth risk for high MOD dyads was 1.4x that of dyads with no outlets (p < 0.001) and 1.2x that of low MOD dyads (p= 0.002). There was no immediate effect on NICU admission risk, but the slope increased 1%/month post-legalization (p < 0.001) including a 1%/month increase for low MOD and 3%/month for high MOD dyads.


Incidence of SGA births in Colorado did not change following recreational marijuana legalization. NICU admissions increased post-legalization.

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Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

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This work was Supported by NIH/NCATS Colorado CTSI Grant Number ULI TR001082.

Author information

JL is a Pediatric Hospitalist who assisted with study design and data analysis. He has approved the final manuscript as submitted. AM is a biostatistician who assisted with study design and data analysis. She has approved the final manuscript as submitted. AB assisted with study design and data analysis. She has approved the final manuscript as submitted. IF assisted with study design and data analysis. He has approved the final manuscript as submitted. ES assisted with study design and data analysis. She has approved the final manuscript as submitted. EW is a neonatologist who assisted with study design and data analysis. She has approved the final manuscript as submitted.

Conflict of interest

The authors declare that they have no conflict of interest.

Correspondence to Justin Lockwood.

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