The cariotocograph, 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 similar to a Doppler fetal monitor measures the fetal heartbeat. A pressure-sensitive transducer, called a tocodynamometer (toco), measures the strength and frequency of uterine contractions.