Editor-In-Chief: C. Michael Gibson, M.S., M.D. 
In medicine (obstetrics) cardiotocography (CTG) is a technical means of recording (-graphy) the fetal heartbeat (cardio-) and the uterine contractions (-toco-) during childbirth. CTG can be used to identify signs of fetal distress.
Recordings are done by two separate transducers, one for the measurement of the fetal pulse and a second one for the contractions.
External measurement means taping or strapping the electrodes to the abdominal wall, with the heart electrode overlying the fetal heart and the contraction electrode measuring the tension of the abdominal wall, an indirect measure of the intrauterine pressure.
Internal measurement requires a certain degree of cervical dilatation, as it involves inserting a pressure catheter into the uterine cavity, as well as attaching a scalp electrode to the child's head to adequately measure the pulse. Internal measurement is more precise, and might be preferable when a complicated childbirth is expected.
A typical CTG reading is printed on paper or stored on a computer terminal for later reference.
CTG times the contractions and the variability in the fetal heart rate. Baseline abnormalities in the heart rate (brady- or tachycardia) may be interpreted in the context of the presentation, as may absence of variability in the FHR.
Decelerations (slowing of the fetal heart rate) during a uterine contraction is normal (type 1 deceleration, or type I dips), but further slowing after resolution of the contraction (type II dips) is generally regarded as pathological and may be taken as a sign of fetal distress.