Real-time ultrasound observation of breathing and movements in the fetal lamb

In seven pregnant ewes with catheters chronically implanted in the fetus, real-time ultrasound observations of fetal breathing and body movements were correlated with direct measurements of fetal arterial and tracheal pressures, heart rate, and intrauterine pressure. There was excellent correlation between the ultrasound record of fetal breathing and recordings of intratracheal pressure changes even when breath amplitude was low or frequently was high. Fetal body movements (stretches, rolls, kicks) were observed during both breathing and nonbreathing periods; vigorous movements were accompanied by rapid deflections of the amniotic and tracheal pressure traces. Movement was frequently accompanied by transient increases or decreases in heart rate. The results indicate that real-time ultrasound is an accurate method of observation of fetal movement in pregnant sheep and is particularly valuable when combined with direct measurements of fetal physiologic parameters.