We describe for the first time methadone and EDDP disposition in umbilical cord from opioid-dependent pregnant women receiving methadone-assisted pharmacotherapy. In general, similar concentrations of methadone and EDDP were found in the maternal and fetal ends of the umbilical cords. High inter-individual variability in methadone and EDDP umbilical cord concentrations (%CV 59.8% and 50.2%, respectively) can be explained by differences in maternal methadone doses and duration of dosing; differences in maternal age and race also might play a role in the high inter-individual variability. In general, methadone concentrations were higher than EDDP, with a mean EDDP/methadone concentration ratio of 0.51±0.3.
Methadone concentrations in umbilical cord were positively correlated to methadone mean daily dose, mean dose during the 3rd
trimester and cumulative dose. To our knowledge, dose-concentration relationships for maternal methadone dose and methadone and EDDP umbilical cord concentrations were never reported. However, correlations between maternal methadone dose and methadone concentrations in maternal plasma (37
) and umbilical cord blood (38
) were previously evaluated, reporting discrepant results.
A significant positive correlation also was noted for EDDP umbilical cord concentrations and EDDP/methadone concentration ratios and neonatal length. As previously described, greater maternal methadone doses were associated with higher umbilical cord methadone and EDDP concentrations. We suggest that the positive correlation between EDDP and neonatal length is reflecting an improvement in neonatal outcome in babies from pregnant women receiving appropriate methadone-assisted therapy, and perhaps lower exposure to illicit drugs. Umbilical cord EDDP/methadone ratio also was positively correlated with neonatal length. Methadone placenta accumulation was much higher than for EDDP; therefore, higher methadone doses will also produce greater umbilical cord EDDP/methadone concentration. Supporting our hypothesis, neonates from pregnant women receiving methadone-assisted therapy had improved neonatal growth parameters as compared to those whose mothers abused heroin and did not receive this treatment (42
). Almost a third (31.6%) of newborns were treated for NAS with morphine sulfate drops, which could have influenced NAS scoring for these newborns. Despite treatment potentially lowering peak NAS and altering time to NAS peak, umbilical cord EDDP concentrations and EDDP/methadone concentration ratios were significantly correlated to peak NAS score and time-to-peak NAS score. Therefore, it may be possible to predict NAS intensity based on umbilical cord concentrations.
Umbilical cord concentrations were not previously correlated to neonatal parameters; however, others investigated correlations between neonatal plasma methadone concentrations and NAS intensity. Mack et al. did not find a relationship between neonatal methadone plasma concentrations and NAS intensity (39
). In contrast, Harper et al. (41
) reported a positive correlation between methadone dose or plasma concentration and NAS severity. Our results supported findings of others, where NAS intensity associated with lower neonatal methadone plasma concentrations (38
) a higher rate of decline in neonatal methadone levels (37
), or both (46
Methadone and EDDP concentrations in umbilical cord were compared to matched placenta and meconium concentrations. As in umbilical cord, methadone was the predominant placenta analyte; however, mean placenta methadone concentrations were 10.7±3.6 times as great as those in umbilical cord. Mean EDDP/methadone ratio in placenta was only 0.11±0.05. Umbilical cord EDDP concentrations were about half those in placenta (placenta/umbilical cord EDDP ratio 2.7±2.3). Methadone placental metabolism was reported to be approximately 1% (47
). Although methadone metabolism in umbilical cord may have occurred, it is more likely that the much lower umbilical cord methadone concentrations were due to low placental transfer. This also is supported through in vitro
experimentation by Nekhayeva et al., suggesting placental methadone accumulation (47
). Furthermore, methadone plasma concentrations (70-660 ng/mL) in pregnant women receiving 5 to 100 mg daily methadone doses (37
) were higher than those reported in umbilical cord blood (17-250 ng/mL) (38
), and umbilical cord tissue in our study (29.7-262.2 ng/mL). These methadone concentrations were much lower than those we found in placenta (308-2647 ng/mL), reflecting placental accumulation. As opposed to umbilical cord and placenta, EDDP was the predominant biomarker in meconium. Moreover, concentrations of both analytes in meconium were much higher than those in the other matrices, reflecting meconium accumulation throughout gestation, and subsequent metabolism to the inactive metabolite.
Correlations between methadone and EDDP concentrations in matched umbilical cord, placenta and meconium specimens also were evaluated. Although methadone transfer from placenta appears to be low, placenta and umbilical cord methadone concentrations, and EDDP/methadone ratios were strongly correlated. A statistically significant positive correlation also was found for EDDP umbilical cord concentrations and methadone meconium concentrations. The reason for this correlation is not clear. We hypothesize that higher methadone meconium concentrations result from higher methadone doses and, therefore, higher methadone (and EDDP) concentrations in umbilical cord. Methadone meconium concentrations were significantly correlated to EDDP, but not to methadone umbilical cord concentrations, most likely due to limited methadone placental transfer.
In addition, cocaine and opiate umbilical cord concentrations were determined. BE was found in only one umbilical cord specimen, confirming in utero
cocaine exposure. Likewise, Moore et al. (50
) reported significant BE concentrations in the umbilical cord of a woman with a positive urine cocaine test at delivery. Cocaine was not detected in this umbilical cord. Winecker et al. (51
) analyzed umbilical cord tissue from pregnant women admitting cocaine consumption during gestation, and found BE as the predominant analyte, followed by norcocaine, mOHBE and ecgonine methyl ester; trace amounts of cocaine were only found in one specimen. In the present study, similar BE concentrations were observed in matched placenta specimens, but low cocaine concentrations also were noted. Thus, placental cocaine transfer also appeared to be low. Opiate and metabolite disposition in umbilical cord were not previously quantified. We found morphine concentrations 10 times higher than those of codeine in the only positive opiate umbilical cord specimen, at concentrations comparable to those in the matched placenta specimen.
To evaluate the usefulness of umbilical cord to detect in utero
cocaine and opiate exposure, umbilical cord concentrations were compared to those in matched meconium and urine specimens. Meconium testing identified in utero
cocaine exposure in 11 participants, with 63.7% containing only mOHBE. Although this metabolite was not included in the umbilical cord analytical method, it is unlikely that this analytical difference contributed to fewer umbilical cord positive findings based on Winecker et al. results showing BE as the primary analyte (51
). With regard to opiates, morphine was detected in 8 meconium specimens, one also positive for codeine, while none of the matched umbilical cord specimens were positive. Surprisingly, the matched meconium specimen for the only morphine- and codeine-positive umbilical cord specimen (participant 16) tested negative for opiates. All participants with the last cocaine or opiate positive urine test in the 3rd
trimester had positive meconium results. The drug detection window in umbilical cord could not be established, as matched urine data from the third trimester were not available for the only cocaine and opiate positive umbilical cord specimen (participant 16). Umbilical cord specimens were negative even when the last positive urine test was just 3 or 13 days before delivery (participants 9 and 11), while meconium results (participant 11) indicated maternal cocaine and opiate consumption. These results might reflect a shorter window of drug detection in umbilical cord than in meconium. Sensitive umbilical cord analytical LOQs should have compensated for the much lower drug concentrations in this biological matrix.
Our results demonstrate that meconium detects more easily in utero
drug-exposed neonates than umbilical cord, in contrast to results reported by Montgomery et al. (28
). These authors screened for cocaine, opiates, amphetamines, cannabinoids and phencyclidine in matched meconium and umbilical cord specimens from infants of pregnant women suspected of illicit drug-intake, finding >90% agreement in these matrices for all analytes. This could be due to a short period of time from last maternal drug consumption to delivery for Montgomery's study participants, higher limits of quantification, or few positive specimens. In addition, the authors did not report any data on metabolites analyzed or measured concentrations in each matrix. The authors also extended their findings by screening and confirming 500 umbilical cord specimens from women suspected of illicit drug consumption (52
), obtaining negative and positive predictive values >98% and >70%, respectively, for methamphetamine, cocaine, opiates, cannabinoids and phencyclidine. Their data supported the efficacy of this alternative matrix for detection of fetal drug exposure; however, data were not available to establish the window of drug detection in umbilical cord. Marin et al. (53
) determined nicotine and metabolites in matched meconium and umbilical cord specimens from women with first or second-hand tobacco exposure history during pregnancy. The authors concluded that both specimens could be applied for the detection of in-utero
exposure to nicotine in the third trimester; however, concentrations of all analytes were generally greater in meconium and, specifically, nicotine concentrations were 3.7 to 60.7-fold higher in meconium (mean= 150.8 ng/g; median= 114 ng/g) than in umbilical cord (mean= 4.3 ng/g; median= 3.8 ng/g). These much higher concentrations of parent drug in meconium suggest accumulation of nicotine in this matrix and, therefore, a longer window of detection than in umbilical cord may be expected.