Effect of Passive Smoking in Pregnancy on Neonatal Nucleated Red Blood Cells

We evaluated whether the absolute nucleated red blood cell (RBC) count is elevated in term, appropriate for gestational age (AGA) infants born to women exposed to passive smoking in pregnancy. We compared absolute nucleated RBC counts taken during the first 12 hours of life in 2 groups of term, vaginally delivered infants, 1 group born to mothers who were routinely exposed to tobacco smoke during pregnancy (n = 55) either at home or at the workplace, and the other to mothers who were not routinely exposed to any tobacco smoke (n = 31). We excluded infants of women with conditions known to elevate nucleated RBC counts. There were no differences between groups in birth weight, maternal age, gravidity, parity, maternal analgesia during labor, 1- and 5-minute Apgar scores. Gestational age was minimally higher in the control group (39.6 +/- 1.1 vs 39.2 +/-.8 weeks). The median absolute nucleated RBC count in the passive smoking group was 357 x 10(6)/L (range: 0-5091 x 10(6)/L) versus 237 x 10(6)/L (range: 0-1733 x 10(6)/L) in nonsmoking controls. Stepwise regression analysis that included Apgar scores, gestational age, and the passive smoking status (yes/no) as independent variables showed significant correlation of absolute nucleated RBC count only with the passive smoking status. At birth, term AGA infants born to mothers exposed to passive smoking have increased circulating absolute nucleated RBC counts compared with those of controls. We speculate that passive smoking in pregnancy should be avoided, because it may have subtle negative effects on fetal oxygenation.