TABLE 24-2. Three-Tier Fetal Heart Rate Interpretation System
Include all of the following: • Baseline rate: 110-160 bpm
Baseline FHR variability: moderate
Early decelerations: present or absent
Accelerations: present or absent
Include all FHR tracings not categorized as Category I or III.
of those encountered in clinical care. Examples include any of the following:
Absence of induced accelerations after fetal stimulation Periodic or episodic decelerations
Prolonged deceleration :2 min but < 1 0 min
Variable decelerations with other characteristics, such as slow return to baseline, "overshoots,"
Include either: • Absent baseline FHR variability and any of the following: bpm = beats per minute; FHR = fetal heart rate. Reproduced with permission from Macones GAl Hankins GO, Spong CY, et al: The 2008 National Institute of Child Health and Human Development workshop report on electronic fetal monitoring: update on definitions, interpretation, and research guidelines, Obstet Gynecol. 2008 Sep;1s12(3))661-666.
Sholapurkar (2012) challenged the validity of the threetier system because most abnormal fetal heart rate patterns fall into the indeterminate category II. It was further suggested that this resulted from most fetal heart rate decelerations being inappropriately classiied as variable decelerations due to cord compression. A group of 19 experts led by Clark (2013) observed that more than 80 percent of fetuses have FHR patterns in tier II. hey proposed a management algorithm for these fetuses, however, their hypothetical algorithm was not clinically tested.
Parer and King (2010) compared this situation in the United States with that of other countries in which a consensus on classiication and management has been reached by several professional societies. Some of these include the Royal College of Obstetricians and Gynaecologists, the Society of Obstetricians and Gynaecologists of Canada, the Royal Australian and New Zealand College of Obstetricians and Gynaecologists, and the Japan Society of Obstetrics and Gynecology. These authors further comment that the NICHD three-tier system is inadequate because category II-an indeterminate FHR pattern-contains a vast heterogenous mixture of patterns that prevents development of a management strategy.
Parer and Ikeda (2007) had previously proposed a colorcoded ive-tier system for both FHR interpretation and management. Two subsequent reports have compared the five-and three-tier systems. Bannerman and associates (2011) found that the two systems were similar in fetal heart rate interpretations for tracings that were either very normal or very abnormal. Coletta and coworkers (2012) found that the ive-tier system had better sensitivity than the three-tier system. Elliott and colleagues (2010) used computerization to measure the performance of a ive-tier classiication system but failed to successfully analyze and categorize 2472 fetal heart recordings.
It is apparent that, after 50 years of continuous electronic fetal heart rate monitoring use, there is not a consensus on interpretation and management recommendations for FHR patterns (Parer, 2011).
• Meconium in the Amnionic Fluid
Obstetricians have long realized that meconium during labor is problematic in the prediction of fetal distress or asphxia. Indeed, although 12 to 22 percent oflabors are complicated by meconium, only a few are linked to neonatal mortality. In an investigation from Parkland Hospital, meconium was found to be a "low-risk" obstetrical hazard because the perinatal mortality rate attributable to meconium was only 1 death per 1000 live births (Nathan, 1994).