OBJECTIVE: The null hypothesis of this study is that maternal administration of indomethacin or terbutaline will not affect fetal breathing and body movements. STUDY DESIGN: Thirty patients with a low-risk pregnancy, gestational age 26 to 32 weeks, and no signs of preterm labor were randomly assigned to receive either terbutaline (5 mg), indomethacin (50 mg), or a placebo. Ultrasonographic evaluation of fetal breathing and body movements was performed for 1 hour before and 1 hour after treatment. The total amount of time of fetal breathing and body movements in each group was subject to statistical analysis that included analysis of variance and covariance and a multiple comparison procedure. RESULTS: Indomethacin increased fetal breathing from 20.8 +/- 13.1 minutes to 42.2 +/- 14.8 minutes (p < 0.01), whereas terbutaline increased fetal breathing movements from 19.8 +/- 9.0 minutes to 35.2 +/- 12.4 minutes (p