oxytocin challenge test, a stress test for the assessment of intrauterine function of the fetus and the placenta. It is performed to evaluate the ability of the fetus to tolerate continuation of pregnancy or the anticipated stress of labor and delivery. A dilute IV infusion of oxytocin is begun, regulated by an infusion pump. The uterine activity is monitored with a tocodynamometer, and the fetal heart rate is monitored with an ultrasonic sensor as the uterus is stimulated to contract by the oxytocin. The amount of solution infused is increased as necessary to cause the uterus to contract for 30 to 40 seconds three times every 10 minutes. The fetal heart rate is observed for variability and for the timing of any marked variation from the normal in relation to uterine contractions. Decelerations of the fetal heart rate in certain repeating patterns may indicate fetal distress. One quarter of the infants diagnosed by this method as being in distress are normal. Therefore, other tests of fetal well-being are recommended before performing an emergency cesarean section or induction of labor.
