Expired air carbon monoxide concentration in mothers and their spouses above 5 ppm is associated with decreased fetal growth

Background. Smoking during pregnancy is associated with reduced birthweight; this relation can be reversed by smoking cessation. Some but not all previous studies have shown that smoking reduction (measured as cigarettes/day or urinary cotinine) may also improve birthweight. The relationship between maternal and spousesʹ expired air carbon monoxide (CO) concentrations (EACO) on fetal growth has not yet been evaluated. Methods. Eight hundred fifty-six smoking and nonsmoking pregnant women were followed during their pregnancy. Their EACO was determined in the first trimester and during delivery. The spousesʹ EACO were also measured at delivery. The main outcome measure was the infantsʹ birthweight. Secondary measures included head circumference, Apgar score, and heart rate at delivery. Cord blood fetal carboxyhemoglobin (FCOHb) served as internal control. Results. Birthweight dose-dependently and significantly decreased with increasing level of maternal (0–5: 3406 ± 32; 6–10: 3048 ± 57; 11–20: 2858 ± 54; >20 ppm: 2739 ± 34 g, P < 0.0001) or spousesʹ EACO (0–5: 3546 ±25; 6–10: 3484 ± 51; 11–20: 3309 ± 47; >20 ppm: 3190 ± 57 g, P < 0.0001). Even the birthweight of newborns whose mother had EACO between 6 and 10 ppm was significantly lower than the birthweight of newborns whose mother had an EACO between 0 and 5 ppm. Spousesʹ EACO of delivering women with EACO of 0–5 ppm showed similar effect. Head circumference, Apgar score, and normal term gestational age decreased also significantly with increasing maternal or spousesʹ EACO. Conclusions. Both maternal and spousesʹ EACO measured during delivery, a proxy of EACO during pregnancy, were dose-dependently and inversely associated with fetal growth. Even low maternal (6 to 10 ppm) or spousesʹ (11 to 20 ppm) EACO may be associated with significantly lower birthweight.