[Effects of acute hypoxemia on fetal movement in the fetal lamb]

Chronically instrumented pregnant models were established using 5 Dorset-Rambouillet pregnant ewes with gestational age between 120 and 138 days. Observation of fetal movements were started on the 3rd postoperative day or later when recovery from the surgery to the physiological condition was confirmed by maternal and fetal biophysical parameters. Fetal movements were observed using real-time ultrasound equipment with linear-array transducer placed on the maternal abdomen. Observation encompassed the control period which lasted one hour followed by an experimental period of fetal hypoxemia created by decreasing maternal FIO2. Observation was also continued during the recovery period when the mother was re-exposed to room air. Maternal and fetal samples were periodically obtained during these periods. Frequency of fetal movements was studied in 10 minute periods under the control and hypoxemic conditions. All fetuses exhibited movements during the control period, ranging 1-42 movements/10 minutes, the mean incidence being 16.9 movements/10 minutes. During fetal hypoxemia (average PaO2 decrease: 8.6 mmHg), fetal movements were significantly reduced to 5.5 movements/10 minutes with complete cessation in some cases. In 4 animals which exhibited complete cessation of both fetal movement (FM) and fetal breathing movement (FBM), FBM disappeared before FM, and reappearance of FM was following by FBM during recovery from hypoxemia.