Cardiotocography
Encyclopedia
In medicine
(obstetrics
), cardiotocography (CTG) is a technical means of recording (-graphy) the fetal
heartbeat
(cardio-) and the uterine
contractions
(-toco-) during pregnancy
, typically in the third trimester. The machine used to perform the monitoring is called a cardiotocograph, more commonly known as an electronic fetal monitor (EFM).
The invasive fetal monitoring was invented by Doctors Orvan Hess
and Edward Hon. A refined (antepartal, non-invasive, beat-to-beat) version (cardiotocograph) was later developed for Hewlett Packard
by Dr. Konrad Hammacher.
s, one for the measurement of the fetal
heart rate
and a second one for the uterine contractions
. Each of the transducers may be either external or internal.
External measurement means taping or strapping the two sensors to the abdominal
wall. The heart ultrasonic sensor
, similar to a Doppler fetal monitor
, detects motion of the fetal heart. The pressure-sensitive contraction transducer, called a tocodynamometer (toco), measures the tension of the maternal 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 fetal head to adequately measure the electric activity of the fetal heart. Internal measurement is more precise, and might be preferable when a complicated childbirth is expected.
A typical CTG reading is printed on paper and/or stored on a computer for later reference. Use of CTG and a computer network, allows continual remote surveillance: a single obstetrical nurse
, midwife, or obstetrician can watch the CTG traces of multiple patients simultaneously, via a computer station.
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 (AWHONN), the American College of Obstetricians and Gynecologists (ACOG
), and the Society for Maternal-Fetal Medicine.
The Royal College of Obstetricians and Gynaecologists
and the Society of Obstetricians and Gynaecologists of Canada
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:
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:
The baseline FHR is determined by approximating the mean FHR rounded to increments of 5 beats per minute (bpm) during a 10-minute window, excluding accelerations and decelerations and periods of marked FHR variability (greater than 25 bpm). There must be at least 2 minutes of identifiable baseline segments (not necessarily contiguous) in any 10-minute window, or the baseline for that period is indeterminate. In such cases, it may be necessary to refer to the previous 10-minute window for determination of the baseline. Abnormal baseline is termed bradycardia when the baseline FHR is less than 110 bpm; it is termed tachycardia when the baseline FHR is greater than160 bpm.
Baseline FHR variability is determined in a 10- minute window, excluding accelerations and decelerations. Baseline FHR variability is defined as fluctuations in the baseline FHR that are irregular in amplitude and frequency. The fluctuations are visually quantitated as the amplitude of the peak- to-trough in bpm. Using this definition, the baseline FHR variability is categorized by the quantitated amplitude as:
A prolonged acceleration is greater than or equal to 2 minutes but less than 10 minutes in duration.
An acceleration lasting greater than or equal to 10 minutes is defined as a baseline change.
Before 32 weeks of gestation, accelerations are defined as having a peak greater than or equal to 10 bpm and a duration of greater than or equal to 10 seconds.
Additionally decelerations can be recurrent or intermittent based on their frequency (more or less than 50% of the time) within a 20 min window.
review has shown that use of cardiotocography reduces the rate of seizure
s in the newborn, but there is no clear benefit in the prevention of cerebral palsy
, perinatal death
and other complications of labour. In contrast, labour monitored by CTG is slightly more likely to result in instrumental delivery (forceps or vacuum extraction) or Cesarean section
. The false-positive rate of cardiotocography for cerebral palsy is given as high as 99%, meaning that only 1-2 of one hundred babies with non-reassuring patterns will develop cerebral palsy. The introduction of additional methods of intrapartum assessment has given mixed results.
When introduced, this practice was expected to reduce the incidence of fetal demise in labor
and make for a reduction in cerebral palsy
(CP). Its use became almost universal for hospital births in the U.S.
In recent years there has been some controversy as to the utility of the cardiotocograph in low-risk pregnancies, and the related belief that over-reliance on the test has led to increased misdiagnoses of fetal distress and hence increased (and possibly unnecessary) cesarean deliveries
.
Medicine
Medicine is the science and art of healing. It encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness....
(obstetrics
Obstetrics
Obstetrics is the medical specialty dealing with the care of all women's reproductive tracts and their children during pregnancy , childbirth and the postnatal period...
), cardiotocography (CTG) is a technical means of recording (-graphy) the fetal
Fetus
A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...
heartbeat
Pulse
In medicine, one's pulse represents the tactile arterial palpation of the heartbeat by trained fingertips. The pulse may be palpated in any place that allows an artery to be compressed against a bone, such as at the neck , at the wrist , behind the knee , on the inside of the elbow , and near the...
(cardio-) and the uterine
Uterus
The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...
contractions
Contraction (childbirth)
-Throughout menstrual cycle:The uterus frequently contracts throughout the entire menstrual cycle, and these contractions have been termed endometrial waves or contractile waves. These appear to involve only the sub-endometrial layer of the myometrium...
(-toco-) during pregnancy
Pregnancy
Pregnancy refers to the fertilization and development of one or more offspring, known as a fetus or embryo, in a woman's uterus. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets...
, typically in the third trimester. The machine used to perform the monitoring is called a cardiotocograph, more commonly known as an electronic fetal monitor (EFM).
The invasive fetal monitoring was invented by Doctors Orvan Hess
Orvan Hess
Orvan Walter Hess was a physician noted for his early use of penicillin and the development of the fetal heart monitor....
and Edward Hon. A refined (antepartal, non-invasive, beat-to-beat) version (cardiotocograph) was later developed for Hewlett Packard
Hewlett-Packard
Hewlett-Packard Company or HP is an American multinational information technology corporation headquartered in Palo Alto, California, USA that provides products, technologies, softwares, solutions and services to consumers, small- and medium-sized businesses and large enterprises, including...
by Dr. Konrad Hammacher.
Method
Simultaneous recordings are performed by two separate transducerTransducer
A transducer is a device that converts one type of energy to another. Energy types include electrical, mechanical, electromagnetic , chemical, acoustic or thermal energy. While the term transducer commonly implies the use of a sensor/detector, any device which converts energy can be considered a...
s, one for the measurement of the fetal
Fetus
A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...
heart rate
Heart rate
Heart rate is the number of heartbeats per unit of time, typically expressed as beats per minute . Heart rate can vary as the body's need to absorb oxygen and excrete carbon dioxide changes, such as during exercise or sleep....
and a second one for the uterine contractions
Contraction (childbirth)
-Throughout menstrual cycle:The uterus frequently contracts throughout the entire menstrual cycle, and these contractions have been termed endometrial waves or contractile waves. These appear to involve only the sub-endometrial layer of the myometrium...
. Each of the transducers may be either external or internal.
External measurement means taping or strapping the two sensors to the abdominal
Abdomen
In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...
wall. The heart ultrasonic sensor
Ultrasonic sensor
Ultrasonic sensors work on a principle similar to radar or sonar which evaluate attributes of a target by interpreting the echoes from radio or sound waves respectively. Ultrasonic sensors generate high frequency sound waves and evaluate the echo which is received back by the sensor...
, similar to a Doppler fetal monitor
Doppler fetal monitor
Invented in 1958 by Dr. Edward H. Hon a Doppler fetal monitor or Doppler fetal heart rate monitor is a hand-held ultrasound transducer used to detect the heart beat of a fetus for prenatal care. It uses the Doppler effect to provide an audible simulation of the heart beat. Some models also...
, detects motion of the fetal heart. The pressure-sensitive contraction transducer, called a tocodynamometer (toco), measures the tension of the maternal abdominal wall - an indirect measure of the intrauterine pressure.
Internal measurement requires a certain degree of cervical
Cervix
The cervix is the lower, narrow portion of the uterus where it joins with the top end of the vagina. It is cylindrical or conical in shape and protrudes through the upper anterior vaginal wall...
dilatation, as it involves inserting a pressure catheter into the uterine cavity, as well as attaching a scalp electrode to the fetal head to adequately measure the electric activity of the fetal heart. Internal measurement is more precise, and might be preferable when a complicated childbirth is expected.
A typical CTG reading is printed on paper and/or stored on a computer for later reference. Use of CTG and a computer network, allows continual remote surveillance: a single obstetrical nurse
Obstetrical nursing
Obstetrical nursing, also called perinatal nursing, is a nursing specialty that works with patients who are attempting to become pregnant, are currently pregnant, or are recently delivered. Obstetrical nurses help provide prenatal care and testing, care of patients experiencing pregnancy...
, midwife, or obstetrician can watch the CTG traces of multiple patients simultaneously, via a computer station.
Interpretation
In the US, the Eunice Kennedy Shriver National Institute of Child Health and Human DevelopmentNational Institute of Child Health and Human Development
The Eunice Kennedy Shriver National Institute of Child Health and Human Development , created by Congress in 1962, supports and conducts research on topics related to the health of children, adults, families, and populations...
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 (AWHONN), the American College of Obstetricians and Gynecologists (ACOG
American Congress of Obstetricians and Gynecologists
The American Congress of Obstetricians and Gynecologists , formerly the American College of Obstetricians and Gynecologists, is a professional association of medical doctors specializing in obstetrics and gynecology in the United States. It has a membership of over 55,000 and represents 90 percent...
), and the Society for Maternal-Fetal Medicine.
The Royal College of Obstetricians and Gynaecologists
Royal College of Obstetricians and Gynaecologists
The Royal College of Obstetricians and Gynaecologists is a professional association based in the UK. Its members, including people with and without medical degrees, work in the field of obstetrics and gynaecology, that is, pregnancy, childbirth, and female sexual and reproductive health...
and the Society of Obstetricians and Gynaecologists of Canada
Society of Obstetricians and Gynaecologists of Canada
The Society of Obstetricians and Gynaecologists of Canada is a national medical society in Canada, representing over 3,000 obstetricians/gynecologists, family physicians, nurses, midwives, and allied health professionals in the field of sexual reproductive health...
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:
- Uterine activity (contractions)
- Baseline fetal heart rate (FHR)
- Baseline FHR variability
- Presence of accelerations
- Periodic or episodic decelerations
- Changes or trends of FHR patterns over time.
Uterine activity
There are several factors used in assessing uterine activity.- Frequency- the amount of time between the start of one contraction to the start of the next contraction.
- Duration- the amount of time from the start of a contraction to the end of the same contraction.
- Intensity- a measure of how strong a contraction is. 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.
- 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- less than or equal to 5 contractions in 10 minutes, averaged over a 30-minute window
- Tachysystole- 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:The baseline FHR is determined by approximating the mean FHR rounded to increments of 5 beats per minute (bpm) during a 10-minute window, excluding accelerations and decelerations and periods of marked FHR variability (greater than 25 bpm). There must be at least 2 minutes of identifiable baseline segments (not necessarily contiguous) in any 10-minute window, or the baseline for that period is indeterminate. In such cases, it may be necessary to refer to the previous 10-minute window for determination of the baseline. Abnormal baseline is termed bradycardia when the baseline FHR is less than 110 bpm; it is termed tachycardia when the baseline FHR is greater than160 bpm.
Baseline FHR variability
The NICHD nomenclature defines baseline FHR variability as:Baseline FHR variability is determined in a 10- minute window, excluding accelerations and decelerations. Baseline FHR variability is defined as fluctuations in the baseline FHR that are irregular in amplitude and frequency. The fluctuations are visually quantitated as the amplitude of the peak- to-trough in bpm. Using this definition, the baseline FHR variability is categorized by the quantitated amplitude as:
- Absent- undetectable
- Minimal- greater than undetectable, but less than or equal to 5 bpm
- Moderate- 6 bpm - 25 bpm
- Marked- greater than 25 bpm
Accelerations
The NICHD nomenclature defines an acceleration as a visually apparent abrupt increase in FHR. An abrupt increase is defined as an increase from the onset of acceleration to the peak in less than or equal to 30 seconds. To be called an acceleration, the peak must be greater than or equal to 15 bpm, and the acceleration must last greater than or equal to 15 seconds from the onset to return.A prolonged acceleration is greater than or equal to 2 minutes but less than 10 minutes in duration.
An acceleration lasting greater than or equal to 10 minutes is defined as a baseline change.
Before 32 weeks of gestation, accelerations are defined as having a peak greater than or equal to 10 bpm and a duration of greater than or equal to 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.- Early Deceleration: Visually apparent, usually symmetrical, gradual decrease and return of the FHR associated with a uterine contraction. A gradual FHR decrease is defined as one from the onset to the FHR nadir of greater than or equal to 30 seconds. The decrease in FHR is calculated from the onset to the nadir of the deceleration. The nadir of the deceleration occurs at the same time as the peak of the contraction. In most cases the onset, nadir, and recovery of the deceleration are coincident with the beginning, peak, and ending of the contraction, respectively
- Late Deceleration: Visually apparent usually symmetrical gradual decrease and return of the FHR associated with a uterine contraction. A gradual FHR decrease is defined as from the onset to the FHR nadir of greater than or equal to 30 seconds. The decrease in FHR is calculated from the onset to the nadir of the deceleration. The deceleration is delayed in timing, with the nadir of the deceleration occurring after the peak of the contraction. In most cases, the onset, nadir, and recovery of the deceleration occur after the beginning, peak, and ending of the contraction, respectively.
- Variable Deceleration: Visually apparent abrupt decrease in FHR. An abrupt FHR decrease is defined as from the onset of the deceleration to the beginning of the FHR nadir of less than 30 seconds. The decrease in FHR is calculated from the onset to the nadir of the deceleration. The decrease in FHR is greater than or equal to 15 beats per minute, lasting greater than or equal to 15 seconds, and 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 prolonged deceleration is present when there is a visually apparent decrease in FHR from the baseline that is greater than or equal to 15 bpm, lasting greater than or equal to 2 minutes, but less than 10 minutes. A deceleration that lasts greater than or equal to 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 min window.
FHR pattern classification
The NICHD workgroup proposed terminology of a three-tiered system to replace the older undefined terms "reassuring" and "nonreassuring".- 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 110-160 bpm,
- 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, but evaluation and continued surveillance and reevaluations are indicated.
- 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 or variable decelerations or bradycardia; or
- Sinusoidal fetal heart rate.
Effect on management
A Cochrane CollaborationCochrane Collaboration
The Cochrane Collaboration is a group of over 28,000 volunteers in more than 100 countries who review the effects of health care interventions tested in biomedical randomized controlled trials. A few more recent reviews have also studied the results of non-randomized, observational studies...
review has shown that use of cardiotocography reduces the rate of seizure
Seizure
An epileptic seizure, occasionally referred to as a fit, is defined as a transient symptom of "abnormal excessive or synchronous neuronal activity in the brain". The outward effect can be as dramatic as a wild thrashing movement or as mild as a brief loss of awareness...
s in the newborn, but there is no clear benefit in the prevention of cerebral palsy
Cerebral palsy
Cerebral palsy is an umbrella term encompassing a group of non-progressive, non-contagious motor conditions that cause physical disability in human development, chiefly in the various areas of body movement....
, perinatal death
Perinatal mortality
Perinatal mortality , also perinatal death, refers to the death of a fetus or neonate and is the basis to calculate the perinatal mortality rate. Variations in the precise definition of the perinatal mortality exist specifically concerning the issue of inclusion or exclusion of early fetal and...
and other complications of labour. In contrast, labour monitored by CTG is slightly more likely to result in instrumental delivery (forceps or vacuum extraction) or Cesarean section
Caesarean section
A Caesarean section, is a surgical procedure in which one or more incisions are made through a mother's abdomen and uterus to deliver one or more babies, or, rarely, to remove a dead fetus...
. The false-positive rate of cardiotocography for cerebral palsy is given as high as 99%, meaning that only 1-2 of one hundred babies with non-reassuring patterns will develop cerebral palsy. The introduction of additional methods of intrapartum assessment has given mixed results.
When introduced, this practice was expected to reduce the incidence of fetal demise in labor
Childbirth
Childbirth is the culmination of a human pregnancy or gestation period with the birth of one or more newborn infants from a woman's uterus...
and make for a reduction in cerebral palsy
Cerebral palsy
Cerebral palsy is an umbrella term encompassing a group of non-progressive, non-contagious motor conditions that cause physical disability in human development, chiefly in the various areas of body movement....
(CP). Its use became almost universal for hospital births in the U.S.
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
In recent years there has been some controversy as to the utility of the cardiotocograph in low-risk pregnancies, and the related belief that over-reliance on the test has led to increased misdiagnoses of fetal distress and hence increased (and possibly unnecessary) cesarean deliveries
Caesarean section
A Caesarean section, is a surgical procedure in which one or more incisions are made through a mother's abdomen and uterus to deliver one or more babies, or, rarely, to remove a dead fetus...
.
Manufacturer
The popular manufacturers are GE (corometrics), Philips, Huntleigh (Sonicaid), Analogic, Ultrasound Technologies (Seward/Wakeling), Toitu, and Sunray.See also
- Fetal stethoscope
- Nonstress test (NST)Nonstress testA nonstress test is a screening test used in pregnancy. A cardiotocograph is used to monitor the fetal heart rate.-Premise:The premise of the NST is that a well-oxygenated, non-acidemic fetus will spontaneously have temporary increases in the fetal heart rate...
- Biophysical profile (BPP)Biophysical profileA biophysical profile is a prenatal ultrasound evaluation of fetal well-being, involving a scoring system. It is often done when a non-stress test is non reactive, or for other obstetrical indications.-The test:...