Despite its limitations, fetal heart rate (FHR) tracing analysis is the best monitor of fetal well being during labor. Typically, continuous electronic fetal monitoring is via transabdominal ultrasound (CTG: cardiotocograph). A transducer is strapped to the maternal abdomen and positioned in such a way to detect fetal rather than maternal heart rate. There are occasional periods of signal loss as the patient or her fetus moves, as well as times when the monitor incorrectly records the maternal signal. Maternal obesity presents particular challenges to non-invasive monitoring.