Multiple birth concordance of street drug assays of meconium analysis

To determine the prevalence of maternal drug usage in a mid-size midwestern city (population 250,000), we analyzed 1,175 consecutive meconium samples from the neonatal intensive care unit from March 1991 through December 1993. We focused on meconium assays from multiple births as a quality control method. Meconium specimens were analyzed using fluorescence polarization immunoassay (FPIA-Abbott Diagnostics) with confirmation done by gas chromatography/mass spectrometry (GC/MS). Cutoff concentrations of 5 ng/g were utilized for all analytes. A total of 151 samples (12.9%) tested positive. Cocaine-exposed neonates had the highest positive rate (63 or 5.4%), followed by marijuana (52 cases or 4.4%), cocaethylene (12 cases or 1%), and amphetamine (1 case or 0.1%). Nine patients (0.8%) had multiple drugs present. There were a total of 23 sets of multiple births (21 twins, 2 triplets); 20 sets of multiple births (42 patients) had concordance with all births testing negative. Three sets of twins had concordance in testing positive, with 1 twin testing positive for cocaine while the other twin tested positive for cocaine and marijuana. No absolute discordance of twins assays were noted. The rate of maternal drug use through measurement of meconium is about 12.95% in this mid-sized midwestern city. Twin studies provide an excellent method for verifying fetal drug exposure. The use of sets of multiple births provides a unique internal quality control mechanism in determining fetal drug exposure.