Assessment of prenatal smoke exposure by determining nicotine and its metabolites in maternal and neonatal urine

Urine specimens were collected from 75 pregnant women before childbirth and from their newborns within 48 postnatal hours. A high-performance liquid chromatography (HPLC) method was used to determine urinary nicotine and its metabolites, cotinine and trans-3'-hydroxycotinine (OH-cotinine) to objectivise prenatal smoke exposure. Using the sum of nicotine metabolites as a marker, 34 women were classed as not exposed to smoke ( < 15 nmol/l), 18 as passive smokers (15-400 nmol/l), and 23 as active smokers ( > 400 nmol/1). The newborns of active smokers exhibited significantly (P < 0.001) higher nicotine metabolite concentrations than did those of either non-exposed women or passive smokers. A close correlation was found to exist between maternal and neonatal nicotine and cotinine concentrations (r=0.8968 and r=0.9205, respectively). For OH-cotinine, this correlation was particularly close when maternal, but not neonatal, OH - cotinine was adjusted to creatinine (r=0.9792). The neonatal/maternal urine concentration ratios for cotinine and OH-cotinine were noted to not significantly depend on the time of postpartal urine collection. Within the first two postnatal days, the extent of current prenatal smoke exposure attributable to active smoking of the mother was best reflected by the urinary concentrations of cotinine plus OH-cotinine without adjustment to creatinine.