Approximately 2.7% of pregnant women reported drinking alcohol during all trimesters of pregnancy, and 7.9% during the third trimester (1). The prevalence of a very serious conglomerate of developmental and cognitive disabilities known as Fetal Alcohol Spectrum Disorders (FASD) is estimated to be as high as 2 to 5% of school-age children, making prenatal alcohol exposure (PAE) the most preventable source of birth defects in the U.S.
Immediate intervention services to the alcohol exposed newborns may be provided through early diagnosis by testing the neonatal specimens. Meconium, one of the specimens of choice, begins formation in fetal intestine between 12 and 16 weeks of pregnancy. It can accumulate ethyl alcohol metabolites, which have been sought as direct PAE biomarkers. Fatty acid ethyl esters (FAEEs) were the first suggested biomarkers with a proposed summed cutoff ranging from 0.5 to 2 nmol/g (2,3). In premature neonates, however, meconium excretion can be prolonged (2), and this can lead to false positive results. In fact, a study has shown that meconium samples collected at least 18 hours after birth from non-exposed neonates contained FAEEs at above 2 nmol/g, even though samples collected at the time of birth were tested negative (2). In the same study, incubation of FAEEs-negative meconium with glucose or ethyl alcohol resulted in significantly elevated concentrations of FAEEs (2). The FAEEs results, therefore, must be interpreted with caution when evaluating prenatal alcohol exposure.
In the recent years, ethyl glucuronide (EtG) and ethyl sulfate (EtS), both ethyl alcohol Phase II metabolites, have been studied as viable biomarkers of PAE (4-7). Based on maternal self report at ≥ 19 weeks’ gestation, EtG at 30 ng/g cutoff showed a higher association with alcohol history compared with FAEEs and EtS (4,5). Also, significant correlation between ethanol dose and EtG concentration was found (5). Since none of the previous studies considered the eventuality of an in vitro EtG formation, we investigated the effects of meconium exposure to environmental alcohol.
Twenty authentic meconium specimens with no detectable EtG were selected at time zero. After being exposed to ethanol (approximately 0.08 g of ethanol in 1 g of meconium) for 24 hours, 18 of the original 20 specimens displayed EtG contents ranging from 107 to 1295 ng/g, well above the recommended 30 ng/g cutoff. For some of the samples the EtG level further increased following additional 24 hours of ethanol incubation. Inter-individual variability of the rate and total amount of in vitro EtG synthesis was also observed. Therefore, the EtG concentration did not correlate with the degree of alcohol exposure. In a similar in vitro experiment, the levels of EtS were found to be only slightly increased, i.e. from non-detectable to 5 – 6 ng/g. Nevertheless, even a slight increase in EtG cutoff to account for possible environmental ethanol exposure could potentially affect the already limited clinical sensitivity of PAE (69.6% at cutoff of 2.5 ng/g EtS) (5).
In conclusion, it is now evident that all ethanol metabolites may form in meconium as a result of either the maternal drinking behavior during pregnancy or other extraneous sources of ethanol exposure after specimen collection. Therefore, meconium should not be regarded as an ideal specimen of choice for testing direct PAE biomarkers.
References
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