One of the central objectives of obstetrical care is the delivery of healthy infants. In modern obstetrics, no tools are relied on more heavily to achieve this objective than monitoring of fetal heart rate and obstetrical ultrasound.
Heart rate monitoring during labor is an attempt to identify fetal oxygen deprivation (and the related acidosis that results from anaerobic metabolism) in its early stages, potentially allowing medical staff to intervene before hypoxic brain injury occurs. Fetal cardiac rate monitoring has been practiced since at least the 1830s, when Kennedy recommended auscultation of the fetal heart using Laennec’s new stethoscope. Eventually it was recognized that certain fetal cardiac rhythms during labor, specifically tachycardia, bradycardia, and transient decreases in pulse rate (ie, “decelerations,” usually either coincident with or delayed in relation to uterine contractions), are associated with neonatal depression and central nervous system injury. The guidelines for intermittent auscultation (listening to the fetal heartbeat for 1 minute every 15-30 minutes during the first stage of labor and every 5 minutes during the second stage; ie, while pushing) were developed in the 1920s. These guidelines and the specialized stethoscope, or fetoscope, used for auscultation remained essentially unchanged until the advent of continuous electronic fetal monitoring (EFM) in the 1970s.