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 or external fetal monitor (EFM). CTG can be used to identify signs of fetal distress.
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.
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Method
Simultaneous recordings are performed by two separate transducers, 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, overlays 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 child's head to adequately measure the pulse. 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 nurse, midwife, or physician can watch the CTG traces of multiple patients simultaneously, via a computer station.
Interpretation
Cardiotocography is used to monitor several different measures: uterine contractions and four fetal heart rate features - baseline heart rate, variability, accelerations, and decelerations.[1] Before interpreting a CTG, it is important to define the risk factors which will influence decision-making, for example any factors why this might be a low- or high-risk pregnancy. In a patient at high-risk for adverse outcome (for example, when the fetus already has intrauterine growth retardation), treatment will probably need to be less expectant (in the example, the decision to proceed to cesarean section might be taken more quickly).
Definitions
- Uterine contractions - time between contractions, which reduces as childbirth progresses; they are quantified as the number of contractions present in a 10 min window and averaged over 30 min. Normal are 5 or less contractions in 10 min; more than 5 contractions in 10 min represents tachysystole.[2]
- Baseline heart rate - average baseline fetal heart rate (normal 110–160).
- Variability - fetal heart rate variability from Baseline per minute (normal 5 - 25).
- Accelerations - increases in fetal heart rate from the baseline by at least 15 beats per minute, lasting for at least 15 seconds. Should be 2 every 20 minutes lasting no longer than 2 minutes. They are normally present, indicating a Reactive Tracing.
- Decelerations (decels) - decreases in fetal heart rate from the baseline by at least 15 beats per minute, lasting for at least 15 seconds. They are normally minimal. There are three types of decelerations, depending on their relationship with uterine contraction:
- Early - begin at start of uterine contraction and end with conclusion of contraction; a sign of increased vagal tone due to fetal head compression.
- Variable - occur at any time irrespective of uterine contractions; a sign of umbilical cord compression.
- Late - begin at the peak of a contraction and ends long after it, hence the "late" when compared to early decels; a sign of fetal hypoxia due to uterus or placental insufficiency - the most worrisome deceleration.
- Additionally decelerations can be recurrent or intermittent based on their frequency (more or less than 50% of the time) within a 20 min window.[2]
- Persistent Tachycardia, when Fetal Heart rate is greater than 160 for more than ten minutes.
- Persistent Bradycardia, when Fetal Heart rate is less than 110 for more than ten minutes.
Significance
The terminology of a three-tiered system replaces the older terms "reassuring" and "nonreassuring".[2]
- Category I (Normal): Tracings with all these findings present are strongly predictive of normal fetal acid-base status 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 evealuation and continued surveillance and reevaluations are indicated:
- Category III (Abnormal): Either tracing predicts abnormal fetal acid-base status; this requires prompt evaluation and management:
- Absence of baseline variability with recurrent late or variable decelerations or bradycardia; or
- Sinusoidal fetal heart rate.
These steps can be remembered with the mnemonic 'DR. C. BRaVADO': Define Risk, Contractions, Baseline Rate, Variability, Accelerations, Decelerations and Outcome.[3][4]
Types of tests
Use of CTG during the third trimester to monitor fetal wellbeing is called a nonstress test. A positive (good) result is indicated by a reactive non-stress test. This means that the fetal heart rate increased (acceleration) by at least 15 beats per minute for at least 15 seconds at least twice during a 20 minute interval.[5]
Use of this machine during labor is called a stress test. 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.[6]
Biophysical profile is another test associated with CTG. It is often done when the non stress test is non reactive.
Effect on management
A Cochrane Collaboration review has shown that use of cardiotocography reduces the rate of seizures 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 caesarian section.[7] The false-positive rate of cardiotocography for cerebral palsy is given as high as 99%, meaning that only 1-2 of one thousand babies with non-reassuring patterns will develop cerebral palsy.[8] The introduction of additional methods of intrapartum assessment has given mixed results.[9]
References
- ^ "Intrapartum Fetal Monitoring". 2008-06-28. http://www.patient.co.uk/showdoc/40000220/. Retrieved 2008-10-11.
- ^ a b c Macones GA, Hankins GD, Spong CY, et al.. "The 2008 National Institute of Child Health and Human Development workshop report on electronic fetal monitoring:update on definitions, interpretation, and research guidelines.". Obstet Gynecol (2008) 112:661-666.
- ^ Dr. C Bravado Poster at the American Academy of Family Physicians.
- ^ Fetal Heart Tracing. Family Practice Notebook.
- ^ London, Marcia; Patrica Ladewig, Jane Ball, & Ruth Bindler (2007). Maternal & Child Nursing Care. Upper Saddle River, NJ: Prentice Hall.
- ^ Goddard, Ros (16 June 2001). "Electronic fetal monitoring Is not necessary for low risk labors". BMJ 322 (322): 1436–1437. doi:. PMID 11408285. http://bmj.bmjjournals.com/cgi/content/full/322/7300/1436. Retrieved 2007-03-02.
- ^ Alfirevic Z, Devane D, Gyte GM (2006). "Continuous cardiotocography (CTG) as a form of electronic fetal monitoring (EFM) for fetal assessment during labour". Cochrane Database Syst Rev 3: CD006066. doi:. PMID 16856111.
- ^ ACOG. "Intrapartum fetal heart rate monitoring. ACOG Practice Bulletin". Obstet Gynecol (2005) 106:1453-60.
- ^ Pettker CM, Lockwood CJ. "New standards for FHR assessment: Something old and something new.". Contemporay OB/GYN (2008) 53:10-12.
See also
External links
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