Contraction Stress Testing

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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.

Objectives of the Test: To assess fetal health and reserve.

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.

Strategies: If uterine contractions are occurring spontaneously, the contraction stress test may proceed directly. To perform the oxytocin challenge test there must be no contraindications to the use of oxytocin. Fetal heart rate and uterine activity monitoring are established and contractions are induced using oxytocin or through intermittent nipple stimulation. Contractions must occur at a rate of three per 10 minutes for at least three 10-minute periods. A normal stress test should show normal fetal heart rate variability and the absence of periodic decelerations. Accelerations with fetal activity are reassuring.

Patient Education: Reassurance; American College of Obstetricians and Gynecologists Patient Education Pamphlet 098 (Special Tests for Monitoring Fetal Health), AP015 (Fetal Heart Rate Monitoring During Labor).

IMPLEMENTATION

Special Considerations: If contractions are occurring spontaneously at a rate of at least three every 10 minutes, the term “contraction stress test” is generally used, whereas the term “oxytocin challenge test” is used when contractions must be induced through oxytocin administration. Like most tests of fetal status, the contraction stress test has a moderate false-positive rate. Consequently, the interpretation of a positive test result must be made in the perspective of other information about the mother and fetus, including the results of other tests such as the nonstress test or biophysical profile. (See also “Antepartum Testing.”)

Freeman RK, Anderson G, Dorchester W. A prospective multi-institutional study of antepartum fetal heart rate monitoring. II. Contraction stress test versus nonstress test for primary surveillance. Am J Obstet Gynecol. 1982;143:778-781.

Knox GE, Huddleston JF, Flowers CEJr. Management of prolonged pregnancy: results of a prospective randomized trial. Am J Obstet Gynecol. 1979;134:376.

Lipitz S, Barkai G, Rabinovici J, Mashiach S. Breast stimulation test and oxytocin challenge test in fetal surveillance: a prospective randomized study. Am J Obstet Gynecol. 1987;157:1178.

Nageotte MP, Towers CV, Asrat T, Freeman RK. Perinatal outcome with the modified biophysical profile. Am J Obstet Gynecol. 1994;170:1672.

Nageotte MP, Towers CV, Asrat T, et al. The value of a negative antepartum test: contraction stress test and modified biophysical profile. Obstet Gynecol. 1994;84:231.

American College of Obstetricians and Gynecologists. Antepartum fetal surveillance. ACOG Practice Bulletin 9. Washington, DC: ACOG, 1999.

American College of Obstetricians and Gynecologists. Management of postterm pregnancy. ACOG Practice Bulletin 55. Obstet Gynecol. 2004;104:639.

Freeman RK. Contraction stress testing for primary fetal surveillance in patients at high risk for uteroplacental insufficiency. Clin Perinatol. 1982;9:265.

Miller DA, Rabello YA, Paul RH. The modified biophysical profile: antepartum testing in the 1990s. Am J Obstet Gynecol. 1996;174:812.

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