Biologic tests detected nearly three times more prenatal cannabis use than self-reports
In a large prospective US cohort, urine and umbilical cord testing detected 75-90% more prenatal cannabis use than self-reports, with younger age, being unmarried, government insurance, and high stress associated with underreporting.
Quick Facts
What This Study Found
Among participants who used cannabis, 74.5% of use at mid-pregnancy and 79.6% at late pregnancy was detected only by urine assay, not self-report. At delivery, 89.7% was detected only by cord assay. Agreement between self-report and biospecimen was fair during pregnancy (Kappa 0.23-0.30) and slight at delivery (Kappa 0.11).
Key Numbers
9,116 participants; 434 (4.76%) used cannabis by either measure. Self-report detected only 25.5% of mid-pregnancy use, 20.4% of late pregnancy use, and 10.3% of delivery use. Kappa agreement: 0.30 at visit 2, 0.23 at visit 3, 0.11 at delivery. Factors associated with discordance: age <30, unmarried, government insurance, moderate/high perceived stress.
How They Did This
Ancillary analysis of the nuMoM2b study, a US multicenter prospective cohort of 9,116 pregnant individuals (2010-2013). Self-reported cannabis use was assessed at three visits. Urine testing for THC metabolite (11-nor-9-carboxy-delta-9-THC) was performed at two visits, and umbilical cord testing at delivery. Agreement was evaluated with Kappa statistics; factors associated with discordance were assessed with multivariable logistic regression.
Why This Research Matters
Research on prenatal cannabis effects relies heavily on self-reported use, but this study shows that self-reports miss the vast majority of actual use. This means virtually all epidemiological studies of cannabis and pregnancy outcomes likely underestimate exposure, potentially diluting observed associations.
The Bigger Picture
The worsening agreement over time (from fair to slight) suggests that as pregnancy progresses, social pressure to deny cannabis use increases. The near-complete reliance on biologic detection at delivery (89.7%) means self-report is essentially useless as a screening tool at that point. This has major implications for clinical screening protocols.
What This Study Doesn't Tell Us
Data from 2010-2013 may not reflect current cannabis use patterns or attitudes post-legalization. Urine testing detects THC metabolites for days to weeks, so positive tests may reflect use before the person knew they were pregnant. The study population was first-time pregnant individuals, which may differ from multiparous populations.
Questions This Raises
- ?Has the gap between self-report and biologic detection changed since cannabis legalization?
- ?Would universal biologic screening during pregnancy be acceptable and feasible?
- ?Are the studies showing minimal prenatal cannabis effects actually measuring much lower exposure than assumed?
Trust & Context
- Key Stat:
- 89.7% of prenatal cannabis use at delivery was detected only by cord testing, not self-report
- Evidence Grade:
- Large multicenter prospective cohort with paired self-report and biologic assays at multiple time points, providing robust data on measurement agreement.
- Study Age:
- Published in 2025, using cohort data from 2010-2013.
- Original Title:
- Self-Reported and Biologic Assessments of Prenatal Cannabis Use: Ancillary Analysis of a Prospective Observational Cohort.
- Published In:
- Substance use & addiction journal, 29767342251389751 (2025)
- Authors:
- Devlin, Paulina M, Allshouse, Amanda A(3), McMillin, Gwen(2), Chung, Judith H, Grobman, William A, Haas, David M, Pippen, Jessica L, Parry, Samuel, Reddy, Uma M, Saade, George R, Simhan, Hyagriv N, Silver, Robert M, Metz, Torri D
- Database ID:
- RTHC-06340
Evidence Hierarchy
Enrolls participants and follows them forward in time.
What do these levels mean? →Frequently Asked Questions
How much cannabis use did self-reports miss?
Self-reports missed about 75% of cannabis use at mid-pregnancy, 80% at late pregnancy, and 90% at delivery compared to biologic testing.
Why do pregnant people underreport cannabis use?
Social stigma, fear of legal or child protective consequences, and healthcare provider disapproval likely contribute. The study found younger age, being unmarried, government insurance, and high perceived stress were associated with underreporting.
Does this mean other studies on prenatal cannabis are wrong?
Not necessarily wrong, but likely underestimating the true prevalence of exposure. If studies classified many actual users as non-users, the real associations between cannabis and pregnancy outcomes could be stronger than reported.
Read More on RethinkTHC
Cite This Study
https://rethinkthc.com/research/RTHC-06340APA
Devlin, Paulina M; Allshouse, Amanda A; McMillin, Gwen; Chung, Judith H; Grobman, William A; Haas, David M; Pippen, Jessica L; Parry, Samuel; Reddy, Uma M; Saade, George R; Simhan, Hyagriv N; Silver, Robert M; Metz, Torri D. (2025). Self-Reported and Biologic Assessments of Prenatal Cannabis Use: Ancillary Analysis of a Prospective Observational Cohort.. Substance use & addiction journal, 29767342251389751. https://doi.org/10.1177/29767342251389751
MLA
Devlin, Paulina M, et al. "Self-Reported and Biologic Assessments of Prenatal Cannabis Use: Ancillary Analysis of a Prospective Observational Cohort.." Substance use & addiction journal, 2025. https://doi.org/10.1177/29767342251389751
RethinkTHC
RethinkTHC Research Database. "Self-Reported and Biologic Assessments of Prenatal Cannabis ..." RTHC-06340. Retrieved from https://rethinkthc.com/research/devlin-2025-selfreported-and-biologic-assessments
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.