Maternal smoking and fetal breathing movements.

Pregnant, habitually smoking women were studied during the last trimester when smoking a standard cigarette, smoking a nontobacco cigarette, or chewing a piece of chewing gum containing 2 or 4 mg. of nicotine. The effects of the experimental interventions were followed on the concentration of nicotine and the percentage of carboxyhemoglobin (COHb) in maternal blood, on the amount and pattern of the fetal breathing movements, and on the maternal heart rate, breathing rate, and blood glucose level. The maternal blood concentration of nicotine was increased by the standard cigarette, the 4 mg. nicotine chewing gum, and the 2 mg. nicotine chewing gum in descending order. The COHb percentage in maternal blood was increased by the standard cigarette and to a lower degree by the nontobacco cigarette. A significant increase of apnea and periodic breathing movements in the fetus followed the smoking of a standard cigarette; a similar but nonsignificant change occurred in a dose-related way after the 4 mg. and the 2 mg. chewing gum. The maternal heart rate was positively correlated to the level of blood breathing movements occurring after smoking one standard cigarette. The suppression of the fetal breathing movements in utero poses the question whether iterated maternal smoking might influence the prenatal assessment of fetal maturity using determination of pulmonary surfactants in the amniotic fluid.