Cardiotocography
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Cardiotocography (CTG) is a technique used to monitor the
fetal heartbeat Heart development, also known as cardiogenesis, refers to the prenatal development of the heart. This begins with the formation of two endocardial tubes which merge to form the tubular heart, also called the primitive heart tube. The heart is t ...
and the
uterine contraction Uterine contractions are muscle contractions of the uterine smooth muscle that occur during the menstrual cycle and labour. Uterine contractions occur throughout the menstrual cycle in the non-pregnant state and throughout gestation. Throughout ...
s during
pregnancy Pregnancy is the time during which one or more offspring develops ( gestates) inside a woman's uterus (womb). A multiple pregnancy involves more than one offspring, such as with twins. Pregnancy usually occurs by sexual intercourse, but ca ...
and
labour Labour or labor may refer to: * Childbirth, the delivery of a baby * Labour (human activity), or work ** Manual labour, physical work ** Wage labour, a socioeconomic relationship between a worker and an employer ** Organized labour and the labour ...
. The machine used to perform the monitoring is called a cardiotocograph. Fetal heart sounds was described as early as 350 years ago and approximately 200 years ago mechanical stethoscopes, such as the
Pinard horn A Pinard horn is a type of stethoscope used to listen to the heart rate of a fetus during pregnancy. It is a hollow horn, often made of wood or metal, about long. It functions similarly to an ear trumpet by amplifying sound. The user holds the wi ...
, were introduced in clinical practice. Modern-day CTG was developed and introduced in the 1950s and early 1960s by Edward Hon, Roberto Caldeyro-Barcia and Konrad Hammacher. The first commercial fetal monitor (Hewlett-Packard 8020A) was released in 1968. CTG monitoring is widely used to assess fetal wellbeing by identifying babies at risk of hypoxia (lack of oxygen). CTG is mainly used during labour. A review found that in the antenatal period (before labour), 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. Up-to-date research is needed to provide more information surrounding this practice. CTG monitoring can sometimes lead to medical interventions which are not necessarily needed.


Methods

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 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 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. 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 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. Internal tocometry can only be used if the
amniotic sac The amniotic sac, also called the bag of waters or the membranes, is the sac in which the embryo and later fetus develops in amniotes. It is a thin but tough transparent pair of membranes that hold a developing embryo (and later fetus) until shor ...
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. A typical CTG reading is printed on paper and may be stored on a computer for later reference. 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 A partogram or partograph is a composite graphical record of key data (maternal and fetal) during labour entered against time on a single sheet of paper. Relevant measurements might include statistics such as cervical dilation, fetal heart rate, d ...
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.


Interpretation

In the US, the
Eunice Kennedy Shriver National Institute of Child Health and Human Development The ''Eunice Kennedy Shriver'' National Institute of Child Health and Human Development (NICHD) is one of the National Institutes of Health (NIH) in the United States Department of Health and Human Services. It supports and conducts research aime ...
sponsored a workshop to develop a standardized nomenclature for use in interpreting Intrapartum fetal heart rate and uterine contraction patterns. This nomenclature has been adopted by the
Association of Women's Health, Obstetric and Neonatal Nurses The Association of Women's Health, Obstetric and Neonatal Nurses (AWHONN) is a 501(c)(3) nonprofit membership organization. The stated purpose of AWHONN is to promote the health of women and newborns. History AWHONN became a separate and indepen ...
(AWHONN), the
American College of Obstetricians and Gynecologists The American College of Obstetricians and Gynecologists (ACOG) is a professional association of physicians specializing in obstetrics and gynecology in the United States. Several Latin American countries are also represented within Districts of ...
(ACOG), and the
Society for Maternal-Fetal Medicine The Society for Maternal-Fetal Medicine was established in 1977 and is a not-for-profit organization of over 5,000 members that are dedicated to improving maternal and child outcomes. The organization's headquarters is located in Washington, D.C. ...
. The
Royal College of Obstetricians and Gynaecologists The Royal College of Obstetricians and Gynaecologists (RCOG) is a professional association based in London, United Kingdom. Its members, including people with and without medical degrees, work in the field of obstetrics and gynaecology, that is ...
and the
Society of Obstetricians and Gynaecologists of Canada The Society of Obstetricians and Gynaecologists of Canada (SOGC) is a national medical society in Canada, representing over 4,000 obstetricians/gynaecologists, family physicians, nurses, midwives, and allied health professionals in the field of s ...
have also published consensus statements on standardized nomenclature for fetal heart rate patterns. Interpretation of a CTG tracing requires both qualitative and quantitative description of several factors. This is commonly summed up in the following acronym, DR C BRAVADO: *DR: Define Risk *C: Contractions (uterine activity) *BRA: Baseline fetal heart rate (FHR) *V: Baseline FHR variability *A: Presence of accelerations *D: Periodic or episodic decelerations *O: Changes or trends of FHR patterns over time


Uterine activity

There are several factors used in assessing uterine activity. *Frequency: the number of contractions per unit time. *Duration: the amount of time from the start of a contraction to the end of the same contraction. *Resting tone: a measure of how relaxed the uterus is between contractions. With external monitoring, this necessitates the use of palpation to determine relative strength. With an IUPC, this is determined by assessing actual pressures as graphed on the paper. *Interval: the amount of time between the end of one contraction to the beginning of the next contraction. The NICHD nomenclature defines uterine activity by quantifying the number of contractions present in a 10-minute window, averaged over 30 minutes. Uterine activity may be defined as: *Normal: 5 or fewer contractions in 10 minutes, averaged over a 30-minute window *
Uterine tachysystole Uterine Tachysystole is a condition of excessively frequent uterine contractions during pregnancy. It is most often seen in induced or augmented labor, though it can also occur during spontaneous labor, and this may result in fetal hypoxia and ac ...
: more than 5 contractions in 10 minutes, averaged over a 30-minute window


Baseline fetal heart rate

The NICHD nomenclature defines baseline fetal heart rate as:


Baseline FHR variability

Moderate baseline fetal heart rate variability reflects the delivery of oxygen to the fetal
central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all par ...
. Its presence is reassuring in predicting an absence of
metabolic acidemia Metabolic acidosis is a serious electrolyte disorder characterized by an imbalance in the body's acid-base balance. Metabolic acidosis has three main root causes: increased acid production, loss of bicarbonate, and a reduced ability of the kidneys ...
and
hypoxic Hypoxia means a lower than normal level of oxygen, and may refer to: Reduced or insufficient oxygen * Hypoxia (environmental), abnormally low oxygen content of the specific environment * Hypoxia (medical), abnormally low level of oxygen in the t ...
injury to the fetus at the time it is observed. In contrast, the presence of minimal baseline FHR variability, or an absence of FHR variability, does not reliably predict fetal acidemia or hypoxia; lack of moderate baseline FHR variability may be a result of the fetal sleep cycle, medications, extreme prematurity, congenital anomalies, or pre-existing neurological injury. Furthermore, increased (or marked) baseline FHR variability (see "Zigzag pattern" and "Saltatory pattern" sections below) is associated with adverse fetal and neonatal outcomes. Based on the duration of the change, increased (i.e. marked) baseline variability is divided into two terms: zigzag pattern and saltatory pattern of FHR. The NICHD nomenclature defines baseline FHR variability as:


Zigzag pattern of fetal heart rate

A Zigzag pattern of fetal heart rate (FHR) is defined as FHR baseline amplitude changes of more than 25 beats per minute (bpm) with a minimum duration of 2 minutes and maximum of 30 minutes. However, according to another study, even a >1 min duration of the zigzag pattern is associated with an increased risk of adverse neonatal outcomes. Despite the similarities in the shape of the FHR patterns, the zigzag pattern is distinguished from the saltatory pattern by its duration. According to the
International Federation of Gynaecology and Obstetrics The International Federation of Gynaecology and Obstetrics, usually just FIGO ("fee'go") as the acronym of its French name Fédération Internationale de Gynécologie et d'Obstétrique, is a worldwide non-governmental organisation representing ...
(FIGO), a saltatory pattern is defined as FHR baseline amplitude changes of more than 25bpm with durations of >30 minutes. In a recently published large obstetric cohort study of the zigzag pattern in almost 5,000 term deliveries in
Helsinki University Central Hospital Helsinki University Central Hospital (HUCH; fi, Helsingin seudun yliopistollinen keskussairaala; sv, Helsingfors universitets centralsjukhus) is a hospital network in Finland. It is one of the largest hospitals in Europe. It encompasses 17 hospi ...
, Tarvonen et al. (2020) reported: "ZigZag pattern and late decelerations of FHR were associated with cord blood acidemia, low
Apgar score The Apgar score is a quick way for doctors to evaluate the health of all newborns at 1 and 5 minutes after birth and in response to Neonatal resuscitation, resuscitation. It was originally developed in 1952 by an anesthesiologist at Columbia Univ ...
s, need for intubation and resuscitation, NICU admission and neonatal hypoglycemia during the first 24 hours after birth." Furthermore, the "ZigZag pattern precedes late decelerations, and the fact that normal FHR pattern precedes the ZigZag pattern in the majority of the cases suggests that the ZigZag pattern is an early sign of fetal hypoxia, which emphasizes its clinical importance." Furthermore, in the recent study of 5150 deliveries, the hypoxia-related ZigZag pattern was associated with cord blood acidemia, low 5-min Apgar scores at birth, and need for neonatal resuscitation after birth, indicating increased occurrence of fetal hypoxia in GDM pregnancies.


Saltatory pattern of fetal heart rate

A saltatory pattern of fetal heart rate is defined in cardiotocography (CTG) guidelines by FIGO as fetal heart rate (FHR) baseline amplitude changes of more than 25 beats per minute (bpm) with a duration of >30 minutes. In a 1992 study, the saltatory pattern FHR was defined by O'Brien-Abel and Benedetti as " tal heart baseline amplitude changes of greater than 25bpm with an oscillatory frequency of greater than 6 per minutes for a minimum duration of 1 minute". The
pathophysiology Pathophysiology ( physiopathology) – a convergence of pathology with physiology – is the study of the disordered physiological processes that cause, result from, or are otherwise associated with a disease or injury. Pathology is the ...
of the saltatory pattern is not well-known. It has been linked with rapidly progressing hypoxia, for example due to an
umbilical cord In placental mammals, the umbilical cord (also called the navel string, birth cord or ''funiculus umbilicalis'') is a conduit between the developing embryo or fetus and the placenta. During prenatal development, the umbilical cord is physiologic ...
compression, and it is presumed to be caused by an instability of the fetal
central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all par ...
. In a study by Nunes et al. (2014), four saltatory patterns in CTG exceeding 20 minutes in the last 30 minutes before birth were associated with fetal
metabolic acidosis Metabolic acidosis is a serious electrolyte disorder characterized by an imbalance in the body's acid-base balance. Metabolic acidosis has three main root causes: increased acid production, loss of bicarbonate, and a reduced ability of the kidneys ...
. According to this study, saltatory pattern is a relatively rare condition; only four cases were found from three large databases. In a study by Tarvonen et al. (2019), it was demonstrated that the occurrence of saltatory pattern (already with the minimum duration of 2 minutes) in CTG tracings during labor was associated with fetal hypoxia indicated by high
umbilical vein The umbilical vein is a vein present during fetal development that carries oxygenated blood from the placenta into the growing fetus. The umbilical vein provides convenient access to the central circulation of a neonate for restoration of blood v ...
(UV) blood
erythropoietin Erythropoietin (; EPO), also known as erythropoetin, haematopoietin, or haemopoietin, is a glycoprotein cytokine secreted mainly by the kidneys in response to cellular hypoxia; it stimulates red blood cell production (erythropoiesis) in the bo ...
(EPO) levels and
umbilical artery The umbilical artery is a paired artery (with one for each half of the body) that is found in the abdominal and pelvic regions. In the fetus, it extends into the umbilical cord. Structure Development The umbilical arteries supply deoxygenated b ...
(UA) blood
acidosis Acidosis is a process causing increased acidity in the blood and other body tissues (i.e., an increase in hydrogen ion concentration). If not further qualified, it usually refers to acidity of the blood plasma. The term ''acidemia'' describes t ...
at birth in human fetuses. As saltatory patterns preceded late decelerations of fetal heart rate (FHR) in the majority of cases, saltatory pattern seems to be an early sign of fetal hypoxia. According to the authors, awareness on this gives
obstetrician Obstetrics is the field of study concentrated on pregnancy, childbirth and the postpartum period. As a medical specialty, obstetrics is combined with gynecology under the discipline known as obstetrics and gynecology (OB/GYN), which is a surgi ...
s and
midwives A midwife is a health professional who cares for mothers and newborns around childbirth, a specialization known as midwifery. The education and training for a midwife concentrates extensively on the care of women throughout their lifespan; co ...
time to intensify electronic fetal monitoring and to plan possible interventions before fetal
asphyxia Asphyxia or asphyxiation is a condition of deficient supply of oxygen to the body which arises from abnormal breathing. Asphyxia causes generalized hypoxia, which affects primarily the tissues and organs. There are many circumstances that can i ...
occurs. Due to a standardized terminology and to avoid miscommunication on CTG interpretation, it has been recently proposed in an exhaustive BJOG review of animal and human studies that terms such as saltatory pattern, ZigZag pattern and marked variability should be abandoned, and the common term "increased variability" should be used in clinical CTG guidelines.


Accelerations

The NICHD nomenclature defines an acceleration as a visually apparent abrupt increase in fetal heart rate. An abrupt increase is defined as an increase from the onset of acceleration to the peak in 30 seconds or less. To be called an acceleration, the peak must be at least 15bpm, and the acceleration must last at least 15 seconds from the onset to return to baseline. A ''prolonged acceleration'' is greater than 2 minutes but less than 10 minutes in duration, while an acceleration lasting 10 minutes or more is defined as a baseline change. Before 32 weeks of gestation, accelerations are defined as having a peak of at least 10bpm and a duration of at least 10 seconds.


Periodic or episodic decelerations

Periodic refers to decelerations that are associated with contractions; episodic refers to those not associated with contractions. There are four types of decelerations as defined by the NICHD nomenclature, all of which are visually assessed. *Early decelerations: a result of increased
vagal tone Vagal tone is activity of the vagus nerve, the 10th cranial nerve and a fundamental component of the parasympathetic branch of the autonomic nervous system. This branch of the nervous system is not under conscious control and is largely responsib ...
due to compression of the fetal head during contractions. Monitoring usually shows a symmetrical, gradual decrease and return to baseline of FHR, which is associated with a uterine contraction. A 'gradual' deceleration has a time from onset to nadir of 30 seconds or more. Early decelerations begin and end at approximately the same time as contractions, and the low point of the fetal heart rate occurs at the peak of the contraction. *Late decelerations: a result of
placental insufficiency Placental insufficiency or utero-placental insufficiency is the failure of the placenta to deliver sufficient nutrients to the fetus during pregnancy, and is often a result of insufficient blood flow to the placenta. The term is also sometimes use ...
, which can result in
fetal distress Fetal distress, also known as non-reassuring fetal status, is a condition during pregnancy or labor in which the fetus shows signs of inadequate oxygenation. Due to its imprecision, the term "fetal distress" has fallen out of use in American obstetr ...
. Monitoring usually shows symmetrical gradual decrease and return to baseline of the fetal heart rate in association with a uterine contraction. A 'gradual' deceleration has an onset to nadir of 30 seconds or more. In contrast to early deceleration, the low point of fetal heart rate occurs after the peak of the contraction, and returns to baseline after the contraction is complete. *Variable decelerations: generally a result of
umbilical cord compression Umbilical cord compression is the obstruction of blood flow through the umbilical cord secondary to pressure from an external object or misalignment of the cord itself. Cord compression happens in about one in 10 deliveries. ...
, and contractions may further compress a cord when it is wrapped around the neck or under the shoulder of the fetus. They are defined as abrupt decreases in fetal heart rate, with less than 30 seconds from the beginning of the decrease to the nadir of heart rate. The decrease in FHR is at least 15 beats per minute, lasting at least 15 seconds but less than 2 minutes in duration. When variable decelerations are associated with uterine contractions, their onset, depth, and duration commonly vary with successive uterine contractions. *Prolonged deceleration: a decrease in FHR from baseline of at least 15bpm, lasting at least 2 minutes but less than 10 minutes. A deceleration of at least 10 minutes is a baseline change. Additionally, decelerations can be ''recurrent'' or ''intermittent'' based on their frequency (more or less than 50% of the time) within a 20-minute window.


FHR pattern classification

Before 2008, fetal heart rate was classified as either "reassuring" or "nonreassuring". The NICHD workgroup proposed terminology for a three-tiered system to replace the older, undefined terms. *Category I (Normal): Tracings with all these findings present are strongly predictive of normal fetal acid-base status at the time of observation and the fetus can be followed in a standard manner: **Baseline rate 110–160bpm, **Moderate variability, **Absence of late or variable decelerations, **Early decelerations and accelerations may or may not be present. *Category II (Indeterminate): Tracing is not predictive of abnormal fetal acid-base status. Evaluation and continued surveillance and reevaluations are indicated. **Bradycardia with normal baseline variability **Tachycardia **Minimal or Marked baseline variability of FHR **Accelerations: Absence of induced accelerations after fetal stimulation **Periodic or Episodic decelerations: Longer than 2 minutes but shorter than 10 minutes; recurrent late decelerations with moderate baseline variability **Variable decelerations with other characteristics such as slow return to baseline, overshoots of "shoulders" seen (humps on either side of deceleration) *Category III (Abnormal): Tracing is predictive of abnormal fetal acid-base status at the time of observation; this requires prompt evaluation and management. **Absence of baseline variability, with recurrent late/variable decelerations or bradycardia; or **
Sinusoidal A sine wave, sinusoidal wave, or just sinusoid is a mathematical curve defined in terms of the '' sine'' trigonometric function, of which it is the graph. It is a type of continuous wave and also a smooth periodic function. It occurs often in m ...
fetal heart rate.


Updated 2015 FIGO Intrapartum Fetal Monitoring Guidelines

FIGO has recently modified the guidelines on intrapartum fetal monitoring, proposing the following interpretation: *Normal: No hypoxia or acidosis; no intervention necessary to improve fetal oxygenation state. **Baseline 110–160bpm **Variability 5–25bpm **No repetitive decelerations (decelerations are defined as repetitive when associated with >50% contractions) *Suspicious: Low probability of hypoxia/acidosis, warrants action to correct reversible causes if identified, close monitoring or adjunctive methods. **Lacking at least one characteristic of normality, but with no pathological features. * Pathological: High probability of hypoxia/acidosis, requires immediate action to correct reversible causes, adjunctive methods, or if this is not possible expedite delivery. In acute situations, delivery should happen immediately. ** Baseline <100bpm **Reduced or increased variability or sinusoidal pattern **Repetitive late or prolonged decelerations for >30 min, or >20 min if reduced variability (decelerations are defined as repetitive when associated with >50% contractions) **Deceleration >5 minutes


Benefits

According to the
Cochrane review Cochrane (previously known as the Cochrane Collaboration) is a British international charitable organisation formed to organise medical research findings to facilitate evidence-based choices about health interventions involving health professi ...
from February 2017, CTG was associated with fewer neonatal seizures but it is unclear if it had any impact on long-term neurodevelopmental outcomes. No clear differences in incidence of cerebral palsy, infant mortality, other standard measures of neonatal wellbeing, or any meaningful differences in long-term outcomes could be shown. Continuous CTG was associated with the higher rates of caesarean sections and instrumental vaginal births. The authors see the challenge in how to discuss these results with women to enable them to make an informed decision without compromising the normality of labour. Future research should focus on events that happen in pregnancy and labour that could be the cause of long-term problems for the baby.


See also

*
Fetal stethoscope A Pinard horn is a type of stethoscope used to listen to the heart rate of a fetus during pregnancy. It is a hollow horn, often made of wood or metal, about long. It functions similarly to an ear trumpet by amplifying sound. The user holds the w ...
* Nonstress test (NST) * Biophysical profile (BPP)


References

{{Pregnancy Tests during pregnancy Medical monitoring