Antepartum fetal and maternal carboxyhemoglobin and cotinine levels among cigarette smokers

The objective of this study was to examine the association of carboxyhemoglobin (COHb) and plasma cotinine levels among pregnant women who smoke cigarettes and their fetuses. Fifteen pregnant women who smoked and their fetuses undergoing cordocentesis had blood samples analysed simultaneously for COHb and cotinine. Linear regression was used to test for associations among study variables. Significant maternal-fetal associations were observed both with COHb (r=0.72, p=0.003) and with cotinine (r=0.96, p=0.003). Maternal cotinine levels were correlated with maternal and fetal COHb, levels (r=0.96, p=0.003; r=0.99, p=0.0003, respectively). Fetal cotinine levels were correlated with COHb in maternal and in fetal blood (r=0.81, p=0.0003; r=0.88, p<0.0001, respectively). The strong direct associations of maternal and fetal levels of COHb and cotinine indicate that maternal COHb and cotinine measurements may be interpreted as surrogates of fetal COHb levels. However, the specificity, ex vivo stability and ease of measurement of cotinine offer advantages over using COHb in quantifying fetal CO exposure following maternal cigarette smoking.