Umbilical cord THC positivity rates increased from 40.6% to 46.2% after Illinois legalized recreational cannabis, with significantly higher THC concentrations in positive samples.
obstetricians, neonatologists, cannabis policy researchers, public health officials
What the researchers found
A higher percentage of umbilical cord tissue tested positive for THC after legalization (46.2% vs. 40.6%, p<0.05) and THC concentrations were significantly higher in the post-legalization period (p<0.001). This suggests both more fetuses were exposed and those exposed experienced higher levels.
Why it matters
Umbilical cord tissue provides an objective measure of fetal THC exposure, avoiding the limitations of self-report. This is direct evidence that legalization was associated with increased fetal cannabis exposure.
The numbers in context
811 cords pre-legalization, 2,170 post-legalization. THC positivity: 40.6% vs. 46.2% (p<0.05). THC concentration: significantly higher post-legalization (p<0.001).
How the study worked
Retrospective observational study at a single center comparing umbilical cord tissue THC levels before (Epoch 1: Oct 2018-Jun 2019, n=811) and after (Epoch 2: Jul 2019-Aug 2021, n=2,170) cannabis legalization in Illinois.
What this study cannot tell us
Single center, limiting generalizability. Cannot determine timing, frequency, or mode of cannabis use. THC in cord tissue reflects exposure but not necessarily fetal effects. Pre/post comparison cannot account for secular trends. No clinical outcome data for exposed newborns.
How to read the evidence
Objective biological measure from a large sample, but single-center design and inability to assess clinical outcomes limit to moderate.
When this study was published
Data from October 2018 through August 2021, spanning Illinois legalization.
The bigger picture
The finding that over 40% of cord tissues tested positive for THC even before legalization is itself striking, suggesting prenatal cannabis exposure was already common. Legalization appears to have increased both the prevalence and intensity of exposure.
Questions still open
- What are the clinical outcomes for newborns with higher cord THC concentrations?
- Does the route of cannabis consumption (smoking vs. edibles) affect cord THC levels differently?
Common questions
Did legalization lead to more prenatal cannabis use?
Is THC in umbilical cord tissue harmful?
Read the original research
Impact of Cannabis Legalization on Umbilical Cord Tissue Tetrahydrocannabinol Levels.
American journal of perinatology, 42(9), 1206-1212
Citation
Spence, Kimberly; Milota, Sarah; Buchanan, Paula; Acharya, Nirja; Mathur, Amit M. (2025). Impact of Cannabis Legalization on Umbilical Cord Tissue Tetrahydrocannabinol Levels.. American journal of perinatology, 42(9), 1206-1212. https://doi.org/10.1055/a-2480-3163
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