Contraction Stress Test (CST)

• CST is a prenatal screening test that measures the FHR in response to uterine contractions
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• CST can assess fetal well-being and identify fetal hypoxia or distress
• CST is usually performed after 28 weeks of gestation or earlier if there are risk factors such as diabetes mellitus, hypertension, IUGR, .
• CST involves placing two belts with sensors on the pregnant person’s abdomen: one to monitor the FHR and one to monitor the uterine contractions
• CST requires inducing uterine contractions by either nipple stimulation or intravenous oxytocin infusion
• CST aims to achieve at least three contractions lasting 40 to 60 seconds in a 10-minute period
• CST is interpreted as negative, positive, equivocal, or unsatisfactory
• A negative CST means that there are no late decelerations of the FHR during contractions
• A negative CST indicates adequate fetal oxygenation and normal placental function
• A positive CST means that there are late decelerations of the FHR with at least 50% of contractions
• A positive CST indicates fetal hypoxia and compromised placental function
• An equivocal CST means that there are late decelerations of the FHR with less than 50% of contractions or variable decelerations of the FHR with or without contractions
• An equivocal CST may indicate cord compression, fetal head compression, or mild fetal hypoxia
• An unsatisfactory CST means that there are insufficient contractions or poor quality of FHR tracing
• An unsatisfactory CST requires repeating the test or performing a BPP
• CST has a risk of preterm labor, premature rupture of membranes, infection, bleeding, .