In utero defecation of the nondistressed fetus: a roentgen study in the goat.

An experimental study was performed to investigate gastrointestinal motility and meconium passage, with simultaneous blood gas measurements, in the fetuses of eight pregnant goats at 110 to 114 days' gestation (full term, 147 to 155 days). With the goats under halothane anesthesia, a nasogastric tube and a heparinized central venous catheter were inserted into the fetuses. 24 hours after surgery, 10 mL of gastric juice from the fetus was replaced with a nonhydrosoluble contrast medium, and serial roentgenograms and blood samples (for pH, PO2, and PCO2 measurement) were taken every 4 hours. All fetuses began to pass the contrast medium into the amniotic cavity within 16 to 22 hours, and central venous blood gas values were normal. The results of this study suggest that the fetus, which urinates routinely, also defecates routinely into the amniotic cavity, even in the absence of distress. The increased incidence of meconium staining in fetal distress conditions may be indicative of impaired clearance of amniotic fluid.