In summary, studies have demonstrated that administration of glucose to normal pregnant females resulted in increased fetal breathing movements in the second and third hour of observation if the glucose was given orally or within the first and second hour of observation 30 min following the administration of a 25-g glucose intravenous bolus. No relationship was demonstrated between maternal plasma glucose concentration and fetal breathing rate or the occurrence of fetal hiccoughs. Furthermore, gross fetal body movements were independent of fluctuations in maternal plasma glucose concentration. Although it may be possible that local excess of carbon dioxide produced by increased oxidation of glucose might have stimulated the chemosensitive areas in the brain stem and produced increased fetal breathing activity, the mechanism for the increased fetal breathing following maternal administration of glucose remains to be elucidated. It would seem that in any short-term studies in which fetal breathing, fetal movement, and other fetal biophysical parameters are being recorded, the experimental approach must take into consideration the episodic nature of fetal breathing and gross body movements, the prandial state of the mother, the time of day, and the gestational age at which the studies are performed. The evidence for the clinical usefulness of standardized approaches of looking at fetal breathing in conjunction with other biophysical parameters remains to be presented.