Electronic Fetal Heart Rate Monitoring: The 5-Tier System, Third Edition reviews the practice of fetal heart rate monitoring. Beginning with a description of the anatomy of fetal circulation, placental function as a respiratory organ, and acid-base balance, it also presents normal fetal cardiovascular and cerebral metabolism. In addition, the pathophysiologic mechanisms involved in progressive fetal asphyxia are examined via a review of the seminal animal and human studies conducted in this field. Also included is a brief summary of fetal heart rate monitoring technology currently used in clinical practice and standard nomenclature for fetal heart rate characteristics. Variant fetal heart rate patterns and the underlying physiologic mechanisms are presented as well. The Third Edition summarizes the research identifying the relationship between specific fetal heart rate patterns and an increasing risk of fetal acidemia, including the effect of deceleration depth, duration, and pattern evolution. It also evaluates the scientific basis that supports management algorithms currently in use and recommends the Parer/Ikeda 5-tier system. This algorithm assigns fetal heart rate patterns to 5 categories based on their progressive risk of fetal acidemia and has been tested in several studies. Clinical management using the 5-tier system is presented in detail.