Intrapartum hypoxia causes about 30% of cerebral palsy and 10% of severe mental retardation, according to recent estimates. It is also responsible for an undetermined number of fetal deaths.
Decreases in the oxygen supply can often be detected before it is too late by changes in the fetal heart rate; auscultation of the fetal heart rate with a fetal stethoscope has been done for years. However, studies have shown this method to be subject to error at extremely high and low rates—precisely where it is most important to be accurate. Hence, work began in the late 1950s to design an electronic means of quantitating the fetal heart rate.
The technique has developed and expanded rapidly. As now practiced, electronic monitoring involves either placing electrodes on the fetus' scalp to record the ECG or measuring fetal heartbeat with an ultrasonic transducer placed on the mother's abdomen. Simultaneous measurement of uterine contractions