The Effects of Prenatal Secondhand Smoke Exposure on Preterm Birth and Neonatal Outcomes
Prenatal SHS exposure and neonatal outcomes
Without reservation, maternal-child research has repeatedly demonstrated associations between direct maternal consumption of tobacco products and adverse birth outcomes (Centers for Disease Control and Prevention [CDC], 2006). However, much less is known about how prenatal consumption of SHS in nonsmoking women effects birth outcomes. Using maternal hair nicotine analysis (2 cm segment of hair reflecting two months of exposure in third trimester), only one study linked SHS in nonsmoking women to preterm birth and/or neonatal outcomes. Jaakkola et al. (2001) reported an increase risk of preterm [(OR) = 6.12; 95% CI, 1.31–28.7]; low birth weight [OR was 1.06 (95% CI, 0.96–1.17)] and small-for-gestational-age [1.04 (95% CI, 0.92–1.19)].
Studies reporting on neonatal outcomes in nonsmoking women have generally used shorter periods of prenatal exposure (1–2 days) or based findings on self-report. Jedrychowski et al. (2004; 2009) assessed the effect of prenatal airborne particulate matter (PM2.5) exposure in the second trimester on selected birth outcomes (gestational age, weight, length, and head circumference at birth) and found all were negatively affected by the exposure. Three studies further demonstrated the association between domestic prenatal SHS exposure and lowered mean infant birth weights by 36, 79 and 137 grams, respectively (Goel, Radotra, Singh, Aggarwal, & Dua, 2004; Hegaard, Kjaergaard, Moller, Wachmann, & Ottesen, 2006; Ward, Lewis, & Coleman, 2007). Goel et al. (2004) and Fantuzzi et al. (2007) reported prenatal exposure to ETS contributed to increased risk for preterm birth and severe SGA. Furthermore, a meta analysis examining the relationship between birth outcomes and SHS exposure in nonsmoking women concluded maternal passive smoking in early and mid/late pregnancy led to an increased risk for small-for –gestational age (SGA) infants. (Liu, Chen, He, Ding, & Ling, 2009)
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Methods
Study Design and Participants
A cross-sectional observational study design was used to investigate the relationship between the level of maternal hair nicotine to preterm birth and newborn outcomes. Permission to conduct the study was obtained through the University’s Institutional Review Board (IRB) board. After consent was obtained, trained research assistants administered a health questionnaire, and collected maternal urine and mother-baby hair samples. Participants were offered a choice of a $25 stipend or $25-equivalent of diapers to participate.
In a metropolitan Kentucky birthing center, 210 postpartum mothers (within three days of birth) consented to participate. To be eligible for study inclusion, women had to be ≥18 years with no reported prenatal use of drugs of abuse in their medical records. With an effective sample size of 200 mothers and an alpha level of .05, the power of Pearson’s product moment correlation to detect a significant association as small as .2 was calculated to be at least 80%. Quota sampling was used to ensure a representative distribution of mothers who were smokers, nonsmokers/passive exposed, and nonsmokers/nonexposed during pregnancy.
Data Collection and Measures
Mothers were identified via the Labor and Birth daily census report and approached about participating in postpartum Birthing Center rooms. After obtaining written consent, mothers were asked to complete a questionnaire. Following completion of the questionnaire, trained research assistants collected urine and hair samples.
Smoking validation and SHS assessment
Previously reported high deception rates in self-report of smoking during pregnancy resulted in validation of smoking status using NicAlert, a commercial urine assay, and based on cut-off limits of urine cotinine (NicAlert, 2007). Nonsmokers were defined by urine cotinine ≤ 99 ng/ml (level 00–02). Current smokers were defined by urine cotinine ≥ 100 ng/ml (level 03–06). NicAlert cutoffs for smoking validation are consistent with previous reported urine cotinine ranges (Higgins et al., 2007).
Participants completed a prenatal health and smoking history questionnaire (average completion time: 22 minutes) based on recommendations by the American College of Obstetricians and Gynecologists (ACOG): Smoking Cessation During Pregnancy: A Clinician's Guide to Helping Pregnant Women Quit Smoking and previous published hair sampling studies (Jaakkola & Jaakkola, 1997); (Hahn et al., 2006; Okoli, Hall, Rayens, & Hahn, 2007). Recommended questions included: number of day or hours exposed to smoking in the home, work or vehicle in the past 7 days; number of persons smoking in the home; and information on cosmetic perms, straighteners, bleaching and hair dye. A woman was classified as a self-reported smoker if she responded “yes” to the question, “Have you smoked a cigarette, even a puff, in the past 7 days.” Smoking mothers were asked to classify their daily smoking consumption, within the past 30 days, based on the following 10 categories: <1 cigarette, 1–5, 6–10, 11–15, 16–20, 21–25, 31–35, 36–40, and > 40.
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