Am J Perinatol 2021; 38(01): 065-075
DOI: 10.1055/s-0039-1694793
Original Article

Maternal Marijuana Exposure and Birth Weight: An Observational Study Surrounding Recreational Marijuana Legalization

Heather L. Straub
1   Division of Maternal-Fetal Medicine, University of Colorado, Aurora, Colorado
Jin Mou
2   MultiCare Institute for Research and Innovation, Tacoma, Washington
Kathryn J. Drennan
1   Division of Maternal-Fetal Medicine, University of Colorado, Aurora, Colorado
3   Division of Maternal-Fetal Medicine, University of Rochester, Rochester, New York
Bethann M. Pflugeisen
2   MultiCare Institute for Research and Innovation, Tacoma, Washington
› Author Affiliations


Objective This study aimed to study the relationship between prenatal marijuana and infant birth weight using natural cohorts established before, during and after the 20-month lapse between legalization and legal recreational sales in Washington State.

Study Design Over 5 years, 5,343 pregnant women with documented urine drug screen (UDS) results delivered at Tacoma General Hospital or Good Samaritan Hospital. Maternal medical data were extracted for three delivery cohorts established based on before (T1), during (T2), and after legalization (T3) of recreational marijuana and legalized availability. Univariate and multivariate models were created to study marijuana exposure on infants' birth weight.

Results Marijuana exposure increased the risk of low birth weight (LBW; odds ratio [OR] = 1.42, 95% confidence interval [CI]: 1.01–2.01). This was more pronounced in full-term babies (OR = 1.72, 95% CI: 1.10–2.69), and was independently associated with a higher risk for small for gestational age (SGA; OR = 1.51, 95% CI: 1.49–1.53). The associations between marijuana exposure and SGA were maintained in cohort-specific models (OR = 1.53, 95% CI: 1.01–2.32 for T2, and OR = 1.43, 95% CI: 1.01–2.02 for T3, respectively).

Conclusion Marijuana exposure verified by UDS was associated with LBW and SGA. However, recreational marijuana legalization and availability did not have direct impact on newborns' risk of LBW or SGA.


This study was conducted at MultiCare Health System, Tacoma and Puyallup, Washington. This study was presented in part at the 37th Annual Society for Maternal Fetal Medicine meeting. January 23 to 28, 2017, Las Vegas, NV.

Supplementary Material

Publication History

Received: 12 June 2019

Accepted: 09 July 2019

Article published online:
20 August 2019

© 2020. Thieme. All rights reserved.

Thieme Medical Publishers, Inc.
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