Effects of ritodrine and fetal oxygenation after in utero fetal surgery in sheep

Surgical procedures which involve the pregnant uterus are associated with preterm labor contractions in the postoperative period. Because uterine contractions decrease fetal oxygen tension, we investigated the effect of maternal ritodrine infusion on fetal oxygen consumption in catheterized fetal sheep 5 h postoperatively. During ritodrine infusion, uterine activity promptly abated, but the oxygen tension in the umbilical vein and descending aorta decreased. The arterial-venous oxygen content difference, the umbilical blood flow, and consequently, fetal oxygen consumption did not change significantly. We conclude that fetal oxygenation is not improved by eliminating uterine activity with maternal ritodrine infusion in the postoperative period.