Between 2001 and 2004, 360 women better were enrolled in a randomized trial comparing three interventions for smoking cessation: best-practice (BP) counseling alone, BP plus an ultrasound accompanied by information on the potential harmful effects of smoking on the fetus, and motivational interviewing plus the information-guided ultrasound. Eligible women were those who reported cigarette smoking during the past 7 days and were between 16 and 26 weeks gestation. Women were recruited in Houston and Harris County area Women, Infants, and Children (WIC) centers and by advertisement. Details of the study are reported elsewhere (Stotts et al., 2009). Information on average number of cigarettes per day in the past week was collected by questionnaire and was validated by salivary cotinine on three occasions: (a) baseline (between 16 and 26 weeks gestation), (b) EOP (at approximately 36 weeks), and (c) 6 weeks postpartum.
All participants gave informed consent and the study was approved by the University of Texas Health Science Center Houston Institutional Review Board. Cigarette smoking during pregnancy is thought to contribute to decreased birth weight by two mechanisms, shortened gestation and fetal growth restriction (Kramer, 1987). As the focus of this analysis was fetal growth restriction, only women with full-term (gestational age at delivery ��37 weeks), singleton pregnancies were included to control for reduced birth weight associated with preterm delivery and multifetal gestation.
Other eligibility criteria for this analysis included availability of saliva cotinine measures at the two time points of interest, baseline and EOP, and information on well-established correlates of infant birth weight, including sex of the Anacetrapib infant, maternal age, parity, education, income, and race/ethnicity. Additionally, in a subset of the cohort, information had been collected on maternal prepregnancy weight, height, and predelivery weight for an ancillary study, providing data on prepregnancy body mass index (BMI) and gestational weight gain. Of the 360 women enrolled in the smoking cessation study, 260 met inclusion criteria. Complete cessation was defined as salivary cotinine <15ng/ml, a cutpoint found to have high sensitivity and specificity (Florescu et al., 2009; Wagenknecht, Burke, Perkins, Haley, & Friedman, 1992), and was used in previous research (Peacock et al., 1998). As this study aimed to observe the effect of change in smoking exposure, women who had salivary cotinine values consistent with nonactive smoking at both time points, baseline and EOP, were excluded. Thirty-five met this criterion, bringing the number to 225 for this analysis.