Timing intrapartum management based on the evolution and duration of fetal heart rate patterns

One of the most important challenges in obstetrics is to determine the appropriate time to deliver the fetus without exposing the mother to unnecessary operative interventions. The use of continuous cardiotocography (cCTG) during labor has resulted in dramatic reductions in intrapartum fetal deaths, but fetal central nervous system (CNS) injury and cerebral palsy (CP) rates have remain relatively unchanged as related to the use of cCTG . In our view, this is due to continuing inability to recognize progressive fetal deterioration and intervene promptly prior to the development of fetal CNS injury. Although the 2008 NICHD workshop proposed a 3-tier classification system, most fetuses born with severe (pathologic) acidemia (cord artery pH < 7.00), as well as those who eventually develop CP, will never reach the stage of NICHD Category III fetal heart rate (FHR) pattern. In the present "Clinical Opinion," we promote a concept derived from observations, that the evolution of the FHR changes of the deteriorating fetus can be visually defined by three color "zones" that are clinically recognizable and, therefore, are actionable. In addition, we will review information regarding how long the fetus may be able to tolerate an abnormal FHR pattern before it suffers an adverse perinatal outcome, an area of investigation that has been rarely addressed before. Based on the available evidence, Category III FHR patterns should not be used as screening criteria because of low sensitivity for either fetal CNS injury (45%) or severe (pathologic) fetal acidemia (36-44%). In addition, the duration of the Category III pattern required for the development of severe fetal acidemia is extremely short to allow for a timely preventative operative intervention. On the contrary, the use of our proposed "red" zone, which includes the most advanced stages in the progressive deterioration of Category II patterns and Category III, will identify the overwhelming majority of fetuses who develop severe (pathologic) acidemia (96%) and/or CNS injury during labor (100%); moreover, the detection of fetal jeopardy by the use of the "red" zone occurs much earlier, as compared to using Category III, thus allowing reasonable amount of time for a timely obstetrical intervention. Further research is needed to determine the false positive rate and positive predictive value for a pre-determined period of time in the red zone.