Under what condition is a CST considered positive?

A contraction stress test (CST) is considered positive if late decelerations occur with more than 50% of induced contractions. This finding indicates that the fetus may not be able to tolerate the stress of contractions, suggesting potential compromised fetal well-being. Late decelerations are changes in the fetal heart rate that occur after the peak of a contraction, typically indicating uteroplacental insufficiency, where the fetus is not receiving adequate oxygen supply during the stress of contractions. Thus, a positive CST reflects significant concerns about fetal health, leading to further clinical assessment and possible intervention.

The other conditions presented do not indicate a positive CST. Irregular baseline fetal heart rate does not provide specific information about the fetus's response to contractions. Similarly, the absence of fetal movements does not directly relate to the findings of a CST regarding contractions and could be caused by various factors. Lastly, consistent stabilization of the fetal heart rate would suggest a reassuring outcome rather than a concern, and thus would not correlate with the criteria for a positive CST.