Racial differences in indications for obstetrical toxicology testing and relationship of indications to test results

Despite illicit substance use in pregnancy occurring across all demographic groups, minority pregnant and delivering patients with a low income tend to undergo testing at a higher rate than their counterparts. National guidelines for indications do not exist and ordering of toxicology testing may be applied inequitably.

This study aimed to evaluate whether any documented indications in a large cohort of patients were associated with a positive toxicology test and whether indications for urine toxicology testing were applied consistently to different demographic groups.

This was a retrospective cohort study reviewing pregnant and delivering patients who underwent toxicology testing on obstetrical units at 1 institution from May 30, 2015, to December 31, 2018. Age, race, marital status, median income of residential ZIP code, indications for testing, and test results were collected for each patient by individual chart review. Indications included preterm complications (preterm prelabor rupture of membranes or preterm labor), abruption or hypertension, reported substance use, fetal complications, maternal complications, and none. Multivariate logistic regression models were analyzed for the association between indication and test result and the likelihood of marijuana as the sole positive test result. Logistic regression was used to evaluate the relationship of indication for testing with maternal race.

Among 20,274 births, 551 patients underwent toxicology testing during the study period. No indication for drug toxicology testing was associated with a positive result, except reported current or previous substance use. Compared with White patients, Black and Hispanic women were 4.26 times (95% confidence interval, 2.55-7.09) and 5.75 times (95% confidence interval, 2.89-11.43) more likely to have toxicology testing for an indication other than reported substance use, respectively. Of all patients with positive test results (n=194), 48% tested positive for marijuana only.

Compared with their White counterparts, Black and Hispanic pregnant and delivering patients may be more frequently toxicology tested for indications less clearly associated with illicit substance use. The absence of evidence-based guidelines for toxicology testing on obstetrical units risks inequitable care and stigmatization of patient groups.