Effects of synthetic glucocorticoid administration on human fetal breathing movements at 34 to 35 weeks' gestational age.
Fetal breathing movements were measured in six women who had received exogenous glucocorticoids throughout pregnancy and in whom the endogenous circadian rhythm in cortisol was absent or had been suppressed. Studies were performed for 24-hour observation periods while women received prednisone and then one week later on the same women after equivalent doses of dexamethasone. Fetal breathing movements occurred 29.9% +/- 1.9% of the time in the prednisone-treated group and this was not changed in the same fetuses after dexamethasone treatment. There was a significant increase in the percentage of time spent making breathing movements during the second and third hours following breakfast, lunch, and dinner (P less than 0.001). A fourth peak in fetal breathing activity occurred in the late evening and seemed to be related to the time of the evening glucocorticoid medication. These data were compatible with the hypothesis that maternal glucocorticoid concentrations may influence patterns of fetal breathing movements at 34 to 35 weeks' gestational age.