Agreement between maternal cannabis use during pregnancy according to self-report and urinalysis in a population-based cohort the Generation R Study.
To verify self-reported information on prenatal drug use in urine because reporting in pregnancy is sensitive to stigma and might lead to misclassification. Using semiquantitative immunochemical analysis, the presence of the urinary metabolite (11-nor-Δ9-tetrahydrocannabinol- 9-carboxylic acid) was compared to self-reported prenatal cannabis use. Sensitivity and specificity for self-report and urinalysis outcomes were calculated and Yules Y was used as an agreement measure. Urine samples were available for 3,997 pregnant women. Of these women, 92 reported having used cannabis during pregnancy (2.3%) and 71 had positive urine screens (1.8%). In total 35% of the 92 women with self-reported cannabis use also had a positive urine screen. Positive urines were relatively frequent in women reporting cannabis use before pregnancy only (7.6%) and in women with missing information (2.6%). Sensitivity and specificity of urinalysis compared to self-report were 0.46 and 0.98. Sensitivity and specificity of self-report compared to urinalysis were 0.36 and 0.99. Yules Y amounted to 0.77, indicating substantial agreement between the measures. Our findings illustrate the difficulties in obtaining valid information on prenatal cannabis use. To improve the quality of cannabis use data, we suggest a 2-step approach starting with self-report.