Oxytocin Challenge Test

(Contraction Stress Test)

This test is designed to "predict" how your baby will respond to contractions while in the womb. During labor contractions,  the blood and oxygen supplies are temporarily decreased.  Most babies can recover easily from this;  this test was designed to pinpoint babies who may not.  This is not a routine prenatal test and is usually recommended after unsatisfactory results of a non-stress test or biophysical profile.  Performed after 34 weeks of pregnancy, this is a lengthier test than the non-stress test,  for a pattern of contractions must be induced (usually artificially). The test may take up to two hours.   This test is basically identical to the non-stress test, except for the stimulation of uterine contractions. 

 The hormone oxytocin will be used to stimulate uterine contractions. This hormone may be naturally induced (nipple stimulation) or artificially given (Pitocin through an IV or, occasionally, an injection).  Some practitioners prefer to use IV Pitocin as it can be turned off abruptly should there develop complications or should contractions become too hard.  Once the contractions are established--the ideal is three contractions every 10 minutes-- your baby's heartrate will be monitored by the electronic fetal monitor before, during, and after each contraction.

A normal test result would yield:

• adequate contractions (three every 10 minutes with each being at least 40 seconds long)

• no late decelerations (A late deceleration would be observed after a contraction;  after a contraction the baby's heart rate should rise.  If it does not, it could indicate distress)

If repetitive late decelerations occur, or if decelerations are noted with half or more of the contractions, a positive result would most likely ensue. A positive result will often result in induction of labor, or in some cases of severe distress, an emergency cesarean section. 

This test is associated with the same risks as the non-stress test which include:  possible incorrect interpretations of the test results leading to a higher rate of cesarean sections (see electronic fetal monitoring).  Factors which could interfere with the test's accuracy include: smoking or use of some other drugs,  your position during the test,  obesity,  and in some instances, having an overly full bladder.  Electronic fetal monitoring may also have  possible undiscovered long term effects of doppler forms of ultrasound. Risks to the baby include fetal distress and other medical interventions which are related to the results to the test.  This test often has false-positive results as does the non-stress test. The test may show abnormal decelerations even when the baby is not in distress.

 There are also other risks resulting from the labor simulation.  The oxytocin (either induced or artificially given) sometimes will trigger very strong, long contractions > 90 seconds (hyperstimulation)  or even trigger labor.  Because of these risks, mothers with placenta previa (placenta partially or totally covering cervix), any uterine surgery, prolonged premature rupture of membranes, or an incompetent cervix (with or without a cerclage--closing the cervix with a stitch), should NOT have this test administered.  Those with multiple pregnancies or with a classic cesarean incision (vertical incision) would also not be candidates for this test.  The use of Pitocin also carries its own risks including, but not limited to,  uterine rupture.