A new study finding that samples from maternal urine and the meconium of their newborn babies frequently produce different results is raising more questions about drug testing of pregnant women.
The study found concerningly high rates of disagreement (or “discordance”) in biochemical testing between maternal urine in women with a documented history of or active drug use and the meconium in their newborns. In some cases, such discordance might be triggering the inappropriate intervention of childcare protective services, including the separation of infants from their mothers, according to the researchers, who presented their findings Feb. 4 at the meeting sponsored by the Society for Maternal-Fetal Medicine.
“There’s a very big debate right now in the obstetrics and perinatology communities about the utility of biochemical testing and the identification of high-risk women,” lead author Cassandra Heiselman, DO, MPH, clinical assistant professor in the department of obstetrics, gynecology and reproductive medicine at Stony Brook (N.Y.) University, said in an interview. “We know that each biochemical test has limitations, which can include basically the inability to detect all substances, especially synthetic opioids like fentanyl, [and] the possibility for false results.”
Inaccuracies in testing can potentially result in inappropriate separation of mother and baby. “Careful scrutiny of results is needed,” Dr. Heiselman said.
The Stony Brook team conducted a retrospective cohort study that identified women presenting for delivery from January 2017 to March 2021 with indications for drug testing, including a known history of or current substance use disorder/misuse, and late or no prenatal care. A standardized panel was used for testing maternal urine and newborn meconium.
Urine tests of 327 women resulted in 187 (57%) positive and 98 (30%) negative results, along with 42 (13%) samples with incomplete data, the researchers reported. In contrast, drug testing of newborn meconium was positive in 273 (83%) cases, negative in 42 (13%), and was not performed in 12 (4%) – for a rate of concordance of 41%.
Concordance of urine/meconium occurred more frequently in male newborns (65%), compared with females (35%). “It is unclear biologically why there is such a difference based on the sex of the infants’ test and is an area that needs further investigation,” Dr. Heiselman said.
Comparing urine and meconium tests for 11 substances resulted in 195/483 (40%) concordance, the researchers said; 18% were discordant with positive maternal urine, and 41% were discordant with newborn positive meconium.
Oxycodone and fentanyl were significantly discordant with positive maternal urine. Cannabis use was the most common factor associated with a positive test of meconium, according to the researchers.
“Some studies have shown cannabis use in the second trimester can show up in meconium testing even if the mother has stopped that behavior,” Dr. Heiselman said. “Then there is also cross-reactivity with other substances that can lead to higher false positive results, especially in the urine toxicology.”
The reasons for the discordant results are not clear and vary by substance, Dr. Heiselman said.
“Cannabis and methadone were the significant factors leading to discordance with positive newborn meconium, which may reflect prior use earlier in pregnancy without recent use before delivery,” she said in an interview. “Urine and meconium reflect potentially different timing in perinatal exposure and the potential differences in windows of detection for different substances. Therefore, we would expect some discordance in our comparisons, just not the extent that we saw.”
Some test results might also have been false positives. Many commonly used medications, from cough syrups to proton pump inhibitors, have the potential to generate positive results for illicit drugs, Dr. Heiselman said.
“The issue of discordance is a complex one, where there are limitations of the tests being performed, possible cross-reactivity with false positives, and the difference in what test reflects as far as timing of prenatal exposure. Furthermore, a negative test does not rule out sporadic use, nor does a positive result diagnose substance use disorder or its severity,” she said.