ObjectiveTo investigate the relation between maternal administration of theophylline and breathing movements during late gestation in human fetuses.MethodsAfter a 1-hour control period, 17 women with normally grown fetuses at 33–38 weeks' gestation were given 400 mg of sustained-release theophylline orally. Maternal plasma theophylline and glucose concentrations were measured every hour, and the incidence of fetal breathing movements and breathing rates were measured continuously during the next 8 hours. Results were compared with those of a similar control group that did not receive theoph-ylline.ResultsThe maternal plasma theophylline concentration increased to detectable levels after 1 hour, reached therapeutic levels of 6.9 ± 0.4 μg/mL (standard error of the mean) after 6 hours, and thereafter averaged 8.3 ± 0.3 μg/mL, significantly higher than initial control values (P< .05). The mean glucose concentration was unchanged during the first 6 hours (79.2 ± 1.1 mg/dL) and then decreased somewhat, averaging 75.8 ± 1.1 mg/dL in the 7–8-hour period. The incidence of fetal breathing increased 26.4 ± 1.9% after 5 hours and remained elevated during the next 3 hours at levels significantly higher than in the initial control period (P< .05) and higher than in the control group that did not receive theophylline. The mean hourly breathing rate averaged 40.9 ± 1.3 breaths per minute during the control period and 40.2 ± 1.2 breaths per minute after ingestion of theophylline, a nonsignificant change.ConclusionsIngestion of theophylline by pregnant women in late gestation is associated with an increase in fetal breathing movements. Theophylline has been used widely in the management of asthma in pregnancy, and the assessment of fetal breathing movements is used routinely for evaluation of fetal status. Therefore, account must be taken of changes in breathing movements caused by maternal theophylline administration.