EFFECTS OF TRANSDERMAL NICOTINE OR SMOKING ON NICOTINE CONCENTRATIONSAND MATERNAL-FETAL HEMODYNAMICS

Objective: To compare nicotine concentrations and fetal middle cerebra l artery resistance indices (RIs) during 21-mg transdermal nicotine us e with these values during maternal smoking. Methods: In this randomiz ed, crossover study, participants smoked approximately 20 cigarettes d aily and were between 24 and 36 weeks' gestation. Subjects were random ized to transdermal nicotine or to smoking ad libitum for 8 hours. One week later, they crossed over to the other condition. Maternal plasma nicotine concentrations and hemodynamic measurements were obtained be fore and after the onset of smoking or patch placement. Results: Area under the plasma nicotine concentration-time curve during patch use wa s similar to continued smoking (93 versus 89 ng-hour/mL, respectively) (P = .77). The mean (standard error [SE] change in the middle cerebra l artery RI from baseline to 4 hours later was similar during patch us e and smoking: -.002 (0.008) versus -.02 (0.015), respectively (P = .3 ). The study had greater than 80% power to detect a 25% difference in nicotine concentrations and a change of 2 standard deviations in the m iddle cerebral artery RI between conditions. An unexpected finding was that of a loss of fetal heart rate (FHR) reactivity in 5/8 tracings a fter patch placement versus 1/6 tracings after smoking (P = .12). The baseline FHR increased by a mean (SE) of 8 (4) beats per minute with l oss of reactivity in the patch condition, compared with a decrease of 3 (3) beats per minute without loss of reactivity (P = .05). Conclusio n: Eight-hour use of 21-mg transdermal nicotine yields nicotine concen trations and middle cerebral artery RIs similar to those produced by h ourly smoking in pregnant smokers. (C) 1997 by The American College of Obstetricians and Gynecologists.