Contraction Stress Testing (Oxytocin Challenge Testing)
By the very nature of labor, the rhythmic contractions of the uterus create stress on the fetus. As the uterus contracts, the head of the baby as well as the umbilical cord is compressed. Both of these processes reduce oxygen content or flow to the brain and normally, temporally, reduce the baby’s heart rate. Since the healthy fetus has its own ability to temporarily protect itself from lack of oxygen, (called reserves), the infant can endure this short period of lack of adequate oxygen. If the baby is subjected to prolonged stress or a period of extreme lack of oxygen then the infant’s reserves are depleted and can no longer recover from the contraction of the uterus. This is the basis for the Contraction Stress Test.
The mother is placed on a fetal monitor and an I.V. (intravenous) line is started and a drug known as Pitocin (oxytocin) is administered. Oxytocin is the chemical name for a drug that is known to stimulate uterine contractions. This drug is used to induce labor, augment a labor that is not as effective as it should be or to stimulate uterine contractions for a limited time to perform a Contraction Stress Test.
As the uterus begins to contract, the effect of the contractions on the infant’s heart rate can be measured. If the heart rate reacts to the contraction by slowing down then recovers rapidly when the contraction ceases, returning to its normal rate the baby’s reserves have not been utilized and fetal well being has been confirmed. If however, the heart rate is slow to return, slows too far or fails to react at all, then delivery is imperative.
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