Chapter 186 Contraction Stress Testing
THE CHALLENGE
Fetal health may be assessed using the contraction stress test (also called “oxytocin challenge test”). This test is somewhat analogous to an exercise stress test for the evaluation of adult cardiac function in that problems or weaknesses that are normally compensated for at rest may become apparent with stress. In the contraction stress test, the fetal–placental–maternal unit is stressed through uterine contractions. The resulting periodic deprivation of uterine blood flow can be used to evaluate the robustness of the fetal condition.
Scope of the Problem: Of pregnancies, 3% to 12% are at risk because of gestations that extend beyond term. More pregnancies may be compromised by maternal disease states that affect fetal health or placental function (e.g., hypertension, diabetes) resulting in abnormalities of fetal growth and amniotic fluid volume and other problems.
TACTICS
Relevant Pathophysiology: During uterine contractions, uterine intramural pressure exceeds perfusion pressure, resulting in transient ischemia and loss of blood delivery to the intervillous spaces. When the fetus and placenta are healthy, this loss of blood flow causes no change in fetal tissue oxygenation, and there is no compensatory or reactive change in fetal heart rate. When the fetal–placental or placental–maternal relationships have been degraded, this brief loss of perfusion may be sufficient to cause a reduction in heart rate in the same way as that seen in labor when late decelerations are found.
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