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| |    Contraction Stress Test by Marjorie Greenfield, M.D. reviewed by Laura Jana, M.D., F.A.A.P. While there are many ways to assess the well-being of a fetus in the third trimester, one test can be especially helpful: the contraction stress test (CST). The test uses a fetal monitor to watch the baby's response to contractions. A healthy fetus in good condition will tolerate the mild stress caused by contractions without difficulty. However, a fetus that is getting just barely enough oxygen may demonstrate a certain type of heart-rate change known as late-type decelerations, In which the baby's heart slows down from the stress of the contraction, then recovers back to baseline after a few moments. In this way, a CST is able to check a baby's oxygen reserve. How the CST is performed The fetal monitor is placed so that it picks up both the fetal heart rate and the mother's contractions. If the mother is having contractions on her own (more than three 40-second contractions in a 10-minute time block), the test is done and interpreted, even if the contractions are mild. If she's not experiencing contractions, she can be given pitocin by IV or do a nipple stimulation protocol to create contractions for the test. Usually these contractions are mild and the mother does not experience significant pain during the test. As soon as contractions appear closer together than three in 10 minutes, the test is complete and the pitocin or nipple stimulation protocol is discontinued. If the baby's heart rate stays normal through the contractions, the CST is said to be negative, meaning the baby is in good condition. Stimulating contractions Even though nipple stimulation sounds like a nice, natural way to bring on contractions for this test, many practitioners have found that the contractions sometimes come too quickly and last many minutes, creating enough stress to slow even a healthy baby's heart rate. Although the fetal heart-rate deceleration often resolves when the stimulation is discontinued, it can take a while for the doctors', nurses', and family members' heart rates to return to normal! If nipple stimulation is used to start contractions, it should be done with careful monitoring of the fetal heart and a protocol of slowly increased stimuli, such as starting with just a warm washcloth on the breast. Do not try this test at home. What does a positive CST mean? Interestingly, even though a contraction stress test may be positive, meaning that there are decelerations of the baby's heart rate, the baby still has a good chance of being fine at birth. Many of these babies even go on to tolerate labor without a problem. About half of the babies with a positive contraction stress test, however, will not be able to tolerate the contractions of labor and will need to be delivered by cesarean. Keep in mind that the purpose of the test is to see how the baby is doing in the uterus and to determine if he might be better off outside his mother's body than in.
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