Tobacco consumption during pregnancy is associated with adverse obstetrical and neonatal outcomes, including premature rupture of membranes, placenta previa, placenta abruption, preterm delivery, shortened gestation, fetal growth restriction, and low birth weight (U.S. Department of Health and Human Services, 2004a
). Furthermore, increased risks of behavioral problems, externalizing behaviors, attention deficit hyperactivity disorder, cognitive impairments, and lower academic achievement are observed in prenatally exposed children (Herrmann, King, & Weitzman, 2008
). Thus, identifying affected infants is critical. Meconium analysis for identifying prenatal tobacco exposure has gained in popularity in recent years. The aims of this research were to investigate factors contributing to tobacco biomarker disposition in meconium, evaluate a proposed concentration for differentiating active and nonsmoking mothers, and determine if biomarkers’ presence or concentrations could predict infant outcomes.
As observed for opiates and cocaine (Kacinko et al., 2008
), the timing and magnitude of tobacco exposure during pregnancy impacts the presence of nicotine and metabolites in meconium. Higher daily cigarette consumption and fewer days between last reported cigarette and birth influenced whether drug biomarkers were found in neonatal meconium. Meconium is currently thought to reflect second and third trimester drug and tobacco exposure; however, our data suggest that only third trimester tobacco exposure can be reliably documented in meconium. Previous studies investigating cigarette consumption have not reported specific relationships between number of cigarettes smoked per day and time elapsed between last cigarette and birth. Kohler, Avenarius, Rabsilber, Gerloff, and Jorch (2007)
evaluated meconium results, maternal urine concentrations, and self-reported gestational age at smoking cessation among nine maternal/fetal dyads, yet no clear relationship between the time interval between smoking cessation and birth, presence of nicotine biomarkers in maternal urine at delivery, and positive neonatal meconium were noted.
Additional research is needed to confirm tobacco detection windows observed in this cohort, particularly among women who stop smoking in pregnancy. Of 87 participants, 8 women reportedly ceased tobacco consumption in the first or second trimester and another 6 quit early in the third trimester, more than 1 month before delivery. A larger population of women who successfully stopped smoking during gestation and who were closely monitored with toxicological testing could refine our detection window estimates.
Recently, researchers employed more sensitive and selective procedures allowing quantification of nicotine and its major metabolites, cotinine, and OHCOT in meconium (Gray, Shakleya, & Huestis, 2008
; Kohler et al., 2007
). While others failed to observe nicotine or OHCOT in meconium (Baranowski, Pochopien, & Baranowska, 1998
; Ostrea, Knapp, Romero, Montes, & Ostrea, 1994
), previous data from our laboratory and others demonstrated that nicotine and OHCOT are as prevalent and abundant as cotinine (Gray, Magri, Shakleya, & Huestis, 2008
; Kohler et al.); moreover, an additional 25% of neonates were identified as tobacco exposed by including both nicotine and OHCOT in testing procedures (Gray, Magri, et al.). However, in this cohort, the majority of meconium specimens contained all three tobacco biomarkers. Differences in analyte distribution between studies may be due to maternal cigarette consumption; the women in the current study reported smoking more cigarettes per day than the previous cohort.
Differentiation of active and nonsmoking women by meconium nicotine and/or metabolites’ concentrations also was investigated. Earlier reports, based on cotinine immunoassay, found concentration differences between nonsmokers, passive smokers, and active smokers (Ostrea et al., 1994
; Sherif et al., 2004
), but passive and women smoking <20 cigarettes/day could not be differentiated based on meconium concentrations (Ostrea et al., 1994
). However, more recent research employing more sensitive analytic methodology suggest that active smokers can be differentiated from nonsmokers and environmentally exposed women, but nonsmokers and environmental-exposed women are indistinguishable based on meconium concentrations. Kohler et al. (2007)
clearly identified active smokers from environmentally exposed or nonsmokers, as all meconium specimens from the active smoking group were positive at a 20 pmol/g (~3 ng/g) analytic limit, whereas meconium specimens from environmentally exposed and nonsmoking groups were all negative. Similarly, our laboratory previously proposed a 10 ng/g nicotine, cotinine or OHCOT cutoff to differentiate active smokers from passive or nonsmokers (Gray, Magri, et al., 2008
). In a cohort of Uruguayan women of predominately low economic status, the 10 ng/g cutoff achieved 82.4% sensitivity and 97.0% specificity (Gray, Magri, et al.). Applying the 10 ng/g cutoff in the current investigation yielded 74.6% sensitivity and 100% specificity; lowering the cutoff to the analytic limits of quantification increased sensitivity to 84.1% without changing specificity. We reevaluated the Uruguayan cohort with the 1 ng/g cotinine, 2.5 ng/g nicotine, or 5 ng/g OHCOT concentration cutoff and observed a larger number of false positives and decreasing specificity (78.1%) at the lower cutoffs and no change in sensitivity as compared with maternal self-reported tobacco use. Different maternal interviewing techniques may have contributed to the specificity discrepancies observed in the two populations; the timeline followback interview administered several times during pregnancy in the current study likely generated more accurate responses than a single multiple-choice style postpartum interview employed in the Uruguayan cohort. For future research endeavors, we suggest the lower 2.5 ng/g nicotine, 1 ng/g cotinine, or 5 ng/g OHCOT cutoff for differentiating maternal smoking status. Furthermore, a larger population of environmentally exposed nonsmoking women is needed to confirm the appropriateness of these cutoffs.
The reliance on maternal self-report is a limitation of most prenatal substance use research. The timeline followback is a well-established interview technique effective for several drugs of abuse and various populations (Sobell et al., 1988
), including obstetric patients (Magnusson, Gransson, & Heilig, 2005
; Sarkar et al., 2009
); however, it is not infallible. To facilitate maternal truthfulness, oral fluid specimens were collected for cotinine testing during each interview session. In some instances, cotinine oral fluid concentrations indicated smoking when mothers reported abstinence. It is well established that self-reported tobacco use often is misrepresented by pregnant women (England et al., 2007
; Gray, LaGasse, et al., 2009
). The 10 ng/ml oral fluid cutoff to differentiate smokers from nonsmokers is slightly lower than previous reports by Hegaard, Kjaergaard, Moller, Wachmann, and Ottesen (2007)
, 13 ng/ml; Owen and McNeill (2001)
,14 ng/ml; and Boyd et al. (1998)
, 30 ng/ml but correspond to levels probable for regular nicotine use, as suggested by Etzel (1990)
and Parazzini et al. (1996)
. Furthermore, the 10 ng/ml cutoff was recommended by the Society for Research on Nicotine and Tobacco Subcommittee on Biochemical Verification (Benowitz et al., 2002
Linear relationships between maternal cigarettes smoked in the third trimester and meconium nicotine, cotinine, OHCOT, and total biomarker concentrations were found. To our knowledge, only one other report has evaluated the relationship between the number of maternal cigarettes consumed daily and meconium concentrations, finding a moderate correlation (r = .492–.678) for nicotine, cotinine, OHCOT, and the summed meconium concentrations (Kohler et al., 2007
). Despite finding statistically significant correlations in our data and those of Kohler, predicting the number of cigarettes with meconium concentrations would be difficult given the low correlation coefficients. Furthermore, observing a relationship between maternal consumption and meconium concentrations is in contrast to other studies evaluating how maternal dose is reflected in meconium concentrations; a monitored buprenorphine administration study observed no dose–concentration relationships based on dose per day, cumulative pregnancy dose, or third trimester dose (Kacinko et al., 2008
To date, the relationship between meconium tobacco biomarker concentrations and neonatal outcomes is poorly defined. Only birth weight was shown to negatively correlate with cotinine concentrations (Sherif et al., 2004
), but this finding was not reproduced in earlier research by our laboratory (Gray, Magri, et al., 2008
) and in the current data. Likewise, binomial tobacco biomarker meconium results (positive/negative) have not consistently proven to be effective predictors of growth deficits. Ostrea et al. (2008)
observed no differences in gestational age at birth, birth weight, length, and head circumference based on meconium positivity for tobacco biomarkers, whereas our laboratory observed decreased head circumference when one or more nicotine biomarkers was present (Gray, Magri, et al.). In the present cohort, significantly reduced gestational age, birth weight, and head circumference were noted when meconium specimens contained nicotine, cotinine, or OHCOT.
Other drug classes were assayed in meconium to identify additional drug exposure that could contribute to negative growth outcomes. Three neonates had opioid-positive meconium that was attributable to pain medication given to the mother during extended labor; this peripartum opioid exposure would not be expected to adversely affect development and growth. Only two other neonates had cocaine-positive meconium. The few cocaine-exposed neonates would not meaningfully confound the effects of nicotine. Future research will evaluate the effect of maternal cannabis use on fetal growth with and without concurrent tobacco exposure.
In conclusion, the detection window for tobacco biomarkers in meconium appears to be shorter than currently thought, reliably reflecting only third trimester tobacco exposure. The presence of tobacco biomarkers in meconium predicts reduced gestational age, birth weight, and/or head circumference, but higher concentrations did not imply more severe deficits.