Concordance and discordance between maternal and newborn drug test results

Screening for substance use is recommended during pregnancy, and many clinicians rely on urine drug screening to identify newborns at potential risk for withdrawal.

This study aimed to determine the concordance and discordance rates between maternal and neonatal drug testing at or near the time of delivery.

This retrospective chart review was performed at a single institution that employs universal testing for those who consent. Results of maternal and neonatal urine drug testing via immunoassay at delivery were compared.

Of 1573 singleton pregnancies, 233 mothers (14.8%) had a positive test result for any substance and 102 of their newborns (43.8%) had concordant positive test results. Of the 285 positive maternal test results for individual substances, 133 (46.7%) were concordant with newborn test results. After removing iatrogenic positives, there were 84 truly discordant pairs representing 5.9% of the total cohort of test pairs, but 29.5% of the pairs with maternal positive test results. When considering the outcome of a newborn positive test result, the overall sensitivity and specificity for the maternal test were 21.1% and 85.8%, respectively. The positive and negative predictive values were 46.7% and 96.4%, respectively. After excluding iatrogenic positive test results, the sensitivity and specificity for maternal testing were 97.8% and 99.4%, respectively, and the negative predictive value of maternal testing for all substances approached 100%. A total of 11 pairs of twins had at least 1 twin with a positive drug test result, and of these, 6 twin pairs (54.5%) had drug test results that were discordant from each other.

There is a high rate of iatrogenic discrepancy in maternal and neonatal drug testing. After adjusting for iatrogenic positive test results, the negative predictive value of maternal testing is high. Many discrepancies, such as those in twins, remained unexplained by medication administration, and potential reasons for these discrepancies warrant further investigation.