page_title: Cardiotocography
section_title: Method
hierarchical_section_title: Cardiotocography / Method
caption_attribution_description: English: Schematic explanation of cardiotocography: heart rate (A) is calculated from fetal heart sounds determined by ultrasound, and uterine contractions are measured by a pressure transducer (B). These numbers are represented on a time scale with the help of a running piece of paper, producing a graphical representation.
context_page_description: Cardiotocography is a technical means of recording the fetal heartbeat and the uterine contractions during pregnancy. The machine used to perform the monitoring is called a cardiotocograph, more commonly known as an electronic fetal monitor.
  Fetal monitoring was invented by Doctors Alan Bradfield, Orvan Hess and Edward Hon. A refined version was later developed for Hewlett Packard by Konrad Hammacher.
  CTG monitoring is widely used to assess fetal wellbeing. A review found that in the antenatal period there is no evidence to suggest that monitoring women with high-risk pregnancies benefits the mother or baby although research around this is old and should be interpreted with caution. The same review found that computerised CTG machines resulted in lower numbers of baby deaths than the traditional CTG machines. More up-to-date research is needed to provide more information around this practice.
  CTG monitoring can sometimes lead to medical interventions which are not necessarily needed. Fetal vibroacoustic stimulation has been used to provoke the baby into being more active. This can improve their CTG monitoring so that the mother does not have to be monitored for as long.
context_section_description: External Cardiotocography can be used for continuous or intermittent monitoring. The fetal heart rate and the activity of the uterine muscle are detected by two transducers placed on the mother's abdomen (one above the fetal heart, to monitor heart rate and the other at the fundus of the uterus to measure frequency of contractions). Doppler ultrasound provides the information which is recorded on a paper strip known as a cardiotocograph (CTG). External tocometry is useful in showing the beginning and end of contractions, as well as frequency, but not the strength of contractions. The absolute values of pressure readings on an external tocometer are dependent on position, and are not sensitive in people who are obese. In cases where information on the strength, or precise timing, of contractions is needed, an internal tocometer is more appropriate.
  Internal Cardiotocography uses an electronic transducer connected directly to the fetal scalp. A wire electrode is attached to the fetal scalp through the cervical opening and is connected to the monitor. This type of electrode is sometimes called a spiral or scalp electrode. Internal monitoring provides a more accurate and consistent transmission of the fetal heart rate than external monitoring because factors such as movement do not affect it. Internal monitoring may be used when external monitoring of the fetal heart rate is inadequate, or closer surveillance is needed. Internal tocometry can only be used if membranes (fore-waters) have ruptured either spontaneously or artificially, and the cervix is open.  To gauge the strength of contractions, a small catheter (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/or stored on a computer for later reference. A variety of systems for centralized viewing of CTG have been installed in a large number of maternity hospitals in industrialised countries, allowing simultaneous monitoring of multiple tracings in one or more locations. Display of maternal vital signs, ST signals and an electronic Partogram are available in the majority of these systems. A few of them have incorporated computer analysis of cardiotocographic signals or combined cardiotocographic and ST data analysis.
caption: Schematic explanation of cardiotocography: heart rate (A) is calculated from fetal heart motion determined by ultrasound, and uterine contractions are measured by a Tocodynamometer (B). These numbers are represented on a time scale with the help of a running piece of paper, producing a graphical representation.
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