Editing Cardiotocography (section)

== Methods ==
[[File:Cardiotocography.jpg|thumb|The display of a cardiotocograph. The fetal heartbeat is shown in orange, uterine contractions are shown in green, and the small green numbers (lower right) show the mother's heartbeat.]]
[[File:Cardiotocography sound.wav|thumb|Cardiotocography sound]]
[[File:Cardiotocography diagram.jpg|thumb|400px|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.]]
[[File:CTG Output.jpg|thumb|Normal CTG output for a gravida not in labor]]
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, with one above the fetal heart to monitor heart rate, and the other at the [[Fundus (uterus)|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).<ref name=alfirevic2017>{{Cite journal|last1=Alfirevic|first1=Zarko|last2=Devane|first2=Declan|last3=Gyte|first3=Gillian M. L.|last4=Cuthbert|first4=Anna|date=3 February 2017|title=Continuous cardiotocography (CTG) as a form of electronic fetal monitoring (EFM) for fetal assessment during labour|journal=[[Cochrane Database of Systematic Reviews]]|volume=2|number=2|pages=CD006066|doi=10.1002/14651858.CD006066.pub3|issn=1469-493X|pmid=28157275|pmc=6464257|doi-access=free}}</ref> External tocometry is useful for showing the beginning and end of contractions as well as their frequency, but not the strength of the contractions. The absolute values of pressure readings on an external tocometer are dependent on position and are not sensitive in people who are obese.<ref name=Callahan2013/> In cases where information on the strength or precise timing of contractions is needed, an internal tocometer is more appropriate.<ref name=Callahan2013/>

Internal cardiotocography uses an electronic transducer connected directly to the fetus. A wire electrode, sometimes called a spiral or scalp electrode, is attached to the fetal scalp through the cervical opening and is connected to the monitor. Internal monitoring provides a more accurate and consistent transmission of the fetal heart rate, as unlike external monitoring, it is not affected by factors such as movement. Internal monitoring may be used when external monitoring is inadequate, or if closer surveillance is needed.<ref>{{cite web|url=http://www.hopkinsmedicine.org/healthlibrary/test_procedures/gynecology/external_and_internal_heart_rate_monitoring_of_the_fetus_92,P07776/|title=Types of Fetal Heart Monitoring|website=www.hopkinsmedicine.org|access-date=21 March 2018}}</ref> Internal tocometry can only be used if the [[amniotic sac]] is ruptured (either spontaneously or artificially) and the cervix 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.<ref>{{Cite web |title=External and Internal Heart Rate Monitoring of the Fetus - Health Encyclopedia - University of Rochester Medical Center |url=https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=92&contentid=P07776 |access-date=2022-04-15 |website=www.urmc.rochester.edu}}</ref>

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 installed in 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.<ref>{{cite journal|last1=Nunes|first1=Inês|last2=Ayres-de-Campos|first2=Diogo|last3=Figueiredo|first3=Catarina|last4=Bernardes|first4=João|title=An overview of central fetal monitoring systems in labour |journal=Journal of Perinatal Medicine|volume=41|issue=1|pages=93–99|date=25 July 2012|pmid=23093259|doi=10.1515/jpm-2012-0067|doi-access=free}}</ref><ref>{{Cite web|url=http://pennmedicine.adam.com/content.aspx?productId=14&pid=14&gid=000138|title=Procedures That May Take Place During Labor and Delivery|website=Penn Medicine|publisher=[[University of Pennsylvania]]|url-status=live|archive-url=https://web.archive.org/web/20200727074208/http://pennmedicine.adam.com/content.aspx?productId=14&pid=14&gid=000138|archive-date=2020-07-27}}</ref><ref>{{cite journal|last1=Neilson|first1=James P.|title=Cardiotocography during labour|journal=[[British Medical Journal]]|volume=306|issue=6874|pages=347–348|date=6 February 1993|pmid=8461676|pmc=1676479|doi=10.1136/bmj.306.6874.347|doi-access=free}}</ref><ref name=alfirevic2017/><ref>{{cite journal |last1=Al Wattar |first1=Bassel H. |last2=Honess |first2=Emma |last3=Bunnewell |first3=Sarah |last4=Welton |first4=Nicky J. |last5=Quenby |first5=Siobhan |last6=Khan |first6=Khalid S. |last7=Zamora |first7=Javier |last8=Thangaratinam |first8=Shakila |title=Effectiveness of intrapartum fetal surveillance to improve maternal and neonatal outcomes: a systematic review and network meta-analysis |journal=Canadian Medical Association Journal |date=6 April 2021 |volume=193 |issue=14 |pages=E468–E477 |doi=10.1503/cmaj.202538|pmid=33824144 |pmc=8049638 |doi-access=free }}</ref>