 we propose that in utero exposure to tobacco smoke products places a newborn at risk for persistent pulmonary hypertension of the newborn ( pphn ) . to test this hypothesis , 
 infants with pphn were identified . 
 healthy newborns of similar ethnicity were identified as a comparison group . 
 cord blood cotinine concentrations and maternal questionnaires were obtained . 
 the number of women exposed to tobacco smoke in each group ascertained by questionnaire was borderline significantly different ( 38.7% vs. 20.5% ; p = 0.080 ) 
 . however , more pphn infants had detectable cotinine in their cord blood ( 64.5% vs. 28.2% ; p = 0.002 ) , and the median cotinine concentrations were significantly higher ( 5.2 ng / ml vs. 2 ng / ml ; p = 0.051 ) than the comparison infants . among infants delivered to nonsmoking women , more pphn infants had detectable cotinine ( 50% vs. 19% ; p = 0.015 ) , and the cotinine concentrations were higher ( 3.5 ng / ml vs. 1.65 ng / ml ; p = 0.022 ) than the comparison group . 
 we conclude that active and passive smoking during pregnancy is a risk factor for pphn . 
 therefore , we recommend that pregnant women cease smoking and avoid environmental tobacco smoke . 
 key words . 
 cotinine , newborns , passive , persistent pulmonary hypertension , smoking , tobacco smoke pollution.imagesfigure 1.figure 2.figure 3 . 
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