is open. To gauge the strength of contractions, a small catheter (called an intrauterine pressure catheter or IUPC) is passed into the uterus past the fetus. Combined with an internal fetal monitor, an IUPC may give a more precise reading of the baby's heart rate and the strength of contractions.

A typical CTG reading is printed on paper and may be stored on a computer for later reference. The plotting speed (paper feed) is set at 3 cm/min in the U.S. and 1 cm/min in Europe. A variety of systems for centralized viewing of CTG have been