Cardiotocograph

Overview
The cardiotocograph, more commonly known as an electronic fetal monitor or external fetal monitor (EFM) or non-stress test (NST), is used to monitor a pregnant woman, typically in the third trimester. A cardiotocograph measures simultaneously both the fetal heart rate and the uterine contractions, if any, using two separate disc-shaped transducers laid against the woman's abdomen. An ultrasound transducer measures the fetal heartbeat. A pressure-sensitive transducer, called a tocodynamometer (toco), measures the strength and frequency of uterine contractions.

The cardiotocograph was invented by Doctors Orvan Hess and Edward Hon.

Use of this machine during the third trimester to monitor fetal wellbeing is called a non-stress test (NST). A positive result is indicated by a reactive non-stress test. This means that the fetal heart rate increased (acceleration) by at least 15 bpm for at least 15 seconds at least twice during a 20 minute interval.

Use of this machine during labor is called a stress test. When introduced, this practice was expected to reduce the incidence of fetal demise in labor and make for a reduction in cerebral palsy (CP). Its use became almost universal for hospital births in the U.S. In recent years there has been some controversy as to the utility of the cardiotocograph in low-risk pregnancies, and the related belief that over-reliance on the test has led to increased misdiagnoses of fetal distress and hence increased (and possibly unnecessary) cesarean deliveries.