Heart Rate Patterns of the Fetus

Frederick R. Jelovsek, MD

During labor and delivery, the heartbeat of the baby is monitored in order to make sure that enough blood flow and oxygen are getting through to the unborn fetus. These fetal heart rate patterns can indicate fetal well-being or, conversely, they may indicate fetal distress. If fetal distress is persistent, it may result in permanent brain damage. It is important to define which patterns may indicate problems.

While most women would think that these patterns have been well defined, they are often contraversial among physicians. A blue- ribbon panel has recently reported its findings on interpreting fetal heart rate patterns, National Institure of Child Health and Human Development Research Planning Workshop, Electronic fetal heart rate monitoring: Research guidelines for interpretation, Am J Obstet Gynecol 1997; 177:1385-90. This group convened because in spite of at least 12 scientific controlled trials of the efficacy of fetal heart rate monitoring, fetal heartrate "patterns signifying jeopardy for the fetus and the need for immediate delivery are often inexactly stated and quantitation is rarely included."

Aside from agreeing on some definitions, this committee only agreed on what represents:

1. a normal pattern with a high predictability of a fetus with normal oxygenization
   • baseline rate - greater than 110/minute and less than 160 beats per minute
   • moderate fetal heart rate variability (6-25 beats/minute)
   • presence of accelerations - greater than15 beats/minute increase lasting more than 15 seconds at 32 weeks gestation or more
   • abscence of decelerations
2. abnormal tracings that are predictive of current or impending fetal asphyxia so severe that the fetus is at risk for neurologic and other fetal damage.
   • recurrent (occurring with 50% or more of contractions) late or variable decelerations with absent FHR variability
   • substantial bradycardia (undefined) with absent FHR variability

While your doctor may worry about fetal well-being with heartrate patterns other than the ones above, this expert panel has decided that more research must be done before it is known that the other pattern is reliable enough to take action upon.