Quantification of prenatal marijuana use: evaluation of the correlation between self-report, serum, urine and umbilical cord assays among women delivering at two urban Colorado hospitals

Background and aims: To estimate during pregnancy correlations between frequency of self-reported use of marijuana and quantified marijuana metabolite in biospecimens including urine, sera and umbilical cord homogenate.

Design: Prospective cohort.

Setting: Two urban hospitals in Colorado with legal recreational and medicinal marijuana.

Participants: Pregnant women (<16 weeks gestation) self-reporting marijuana use.

Measurements: Participants completed a written self-report survey and provided biospecimens at <16 weeks gestation (n = 46), 18 to 22 weeks gestation (n = 43), 32 to 36 weeks gestation (n = 39), and delivery (n = 37). Self-reported marijuana use frequency was calculated based on past-month days of use multiplied by number of daily uses. Maternal urine and sera were tested for presence (>5 ng/mL) of 11-nor-9-carboxy-delta-9-tetrahydrocannabinol (THC-COOH). Liquid chromatography tandem mass spectrometry quantified THC-COOH in umbilical cord homogenate (ng/g). Last marijuana use by any measure was recorded to evaluate the time frame over which THC-COOH remains detectable (>0.10 ng/g) in cord.

Findings: From December 2017 through May 2019, 51 pregnant women enrolled, and 46 were included in analyses (2 withdrew and 3 had a spontaneous abortion). The majority were normal weight, White or Black race, and insured by Medicaid. At the time of enrollment between 7 to 15 weeks' gestation, 87% had ongoing use by self-report, or positive urine or serum. The majority (33 [66%]) stopped using before delivery. Sera and urine results were strongly correlated with self-reported use frequency (Spearman correlation coefficient [r] range 0.70-0.87 across visits, P < 0.001), and with each other. There was only one positive cord result when use stopped before 22 weeks. Frequency of self-reported marijuana use at delivery had strong correlation with quantified cord THC-COOH (r = 0.80, 95% CI = 0.62-0.89).

Conclusions: Quantified umbilical cord THC-COOH appears to strongly correlate with frequency of maternal marijuana use in the last month of pregnancy. Earlier use can be measured by either quantitative urine or serum assay.