A dose-response effect has been observed between nicotine exposure in pregnant women and negative effects on neurobehavioral development in children. This may include secondhand smoke (SHS) exposure. Cotinine, a metabolite of nicotine, has a biological half-life of 9 hours in pregnant women and can be used as a biomarker for assessing recent exposure to SHS. Authors of the present study evaluated cotinine levels in 175 nonsmoking mothers, a subset of the Rhea study (a mother-child cohort of 1388 women Crete, Greece), and their infants to examine potential associations between prenatal SHS exposure and neurodevelopmental outcomes in 18-month-old infants. Secondhand smoke questionnaires were completed, and urine samples were collected approximately the 12th and 30th weeks of pregnancy (101 women gave 2 samples, 54 gave 1 sample during visit 1, 20 gave 1 sample during visit 2). Total cotinine levels were measured via gas chromatography/mass spectrometry. At 18 months, a randomly selected group of mothers was contacted to participate in neurodevelopmental assessment of their child. Authors used the Bayley Scales of Infant and Toddler Development, Third Edition (Bayley-III), which assesses cognition, language, receptive/expressive communication, fine and gross motor skills, socioemotion levels, and adaptive behavior. A higher Bayley-III score indicates better functioning.
Overall, on the questionnaire, self-reported maternal SHS exposure at home, in the car, and in other nonpublic places was positively correlated with increased cotinine levels, although in general, cotinine levels were low (mean, 10.3 ng/mL). Exposure at work was not significantly related. In terms of infant exposure, 56% of infants had SHS exposure, with maternal exposure during pregnancy (increased cotinine levels) linked to increased postnatal SHS exposure at home (P = 0.008) or other locations (P = 0.02). In regard to neurodevelopmental assessment of the infant, in both adjusted and unadjusted models, cognition, receptive communication, and gross motor skills (body balance and movement of limbs and torso) were negatively affected by pregnancy cotinine levels. However, only the gross-motor finding, specifically, a 3-point decrease in Bayley-III score, was significant, especially in female infants. Although the clinical impact of a decrease in Bayley Psychomotor Developmental index has not been reported, a similar decrease in Bayley Mental Developmental Index indicates poorer cognitive development in infants. Further studies are needed to explicitly examine this finding and any effects on gross motor development, especially between boys and girls.