The paradox of FHR monitoring
The greatest strength of intrapartum FHR monitoring is the ability of moderate variability or accelerations, or both, to predict normal neurologic outcome with an extremely high degree of reliability.1,11,12 One of the greatest weaknesses of FHR monitoring is the inability of an “abnormal” tracing to predict abnormal neurologic outcome with any clinically relevant degree of accuracy. The false-positive rate of FHR monitoring for predicting cerebral palsy has been reported to exceed 99%, yielding a positive predictive value of less than 1%.1,13 This imprecision is explained in part by the relative rarity of intrapartum hypoxic neurologic injury, and in part by the mitigating interventions that are frequently prompted by FHR “abnormalities.”14 However, these explanations do not alter the fact that the positive predictive value of intrapartum FHR monitoring, as it is used in actual clinical practice, is essentially zero.
Reasonable management decisions simply cannot be based on the results of a test that is virtually always wrong. On the other hand, the negative predictive value of intrapartum FHR monitoring is nearly 100%. A test that is virtually always right is the ideal foundation for rational decision-making.
Standardization of intrapartum FHR monitoring promotes safety by reducing unnecessary complexity and minimizing the error inherent in random recall. However, the technology can achieve its potential only if it is used appropriately. Trying to use intrapartum FHR monitoring to diagnose neurologic injury is a recipe for failure. In contrast, relying on the presence of moderate variability or accelerations, or both, to confirm adequate fetal oxygenation allows the clinician to formulate and articulate a rational, evidence-based plan of management that reflects consensus in the literature.
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