Study Questions Reliability of Maternal Drug Testing

Howard Wolinsky

February 04, 2022

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 February 4 at the 2022 Pregnancy Meeting of the Society for Maternal-Fetal Medicine.

Dr Cassandra Heiselman

"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 the Renaissance School of Medicine at Stony Brook University, Stony Brook, New York, told Medscape Medical News. "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," 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 to 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," 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," 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, 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 told Medscape. "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, 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.

Lack of Standards

Heiselman said states and the federal government lack standards to biochemically evaluate women at risk for drug abuse and their newborns.

"My institution uses a risk-based protocol. Basically, we test cases where we have a known history of substance use disorder or active use, a history in the last 3 years of any kind of substance use, initiation of late prenatal care after 20 weeks, or no prenatal care at all," she said. "And then the pediatricians on the other side will test neonates if the mother has any of that history or if the neonates themselves have unexplained complications or drug withdrawal symptoms."

High rates of discordance can result in the inappropriate intervention by childcare protective service agencies when the mother may not have a substance use disorder, she noted.

Perinatologist Kecia Gaither, MD, MPH, associate professor of clinical obstetrics and gynecology at Weill Cornell Medicine in New York City, called the findings "no surprise," but added that negative findings in neonates "do not exclude the possibility of substance abuse by the mother. It is important to recognize the limitations inherent with screening tests for illicit substances in neonates from substance-abusing mothers."

Heiselman added that understanding what maternal and infant drug tests truly reflect "can help us as clinicians in deciding when we test, whether it's medically necessary, instead of just thinking biochemical tests are the best screening tool, because we know that we are screening. We must engage these women in empathetic and nonjudgmental discussions, which often will elucidate a substance use disorder history more so than just biochemical testing, negative or positive."

The researchers have disclosed no relevant financial relationships.

Society for Maternal-Fetal Medicine (SMFM) 2022 Annual Pregnancy Meeting: Oral Presentation 45.

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