Cardiotocography (CTG; synonyms: cardiotocography, CTG registration, cardiotocogram, cardiac tone contraction recorder; cardio = heart, toko = contraction, and graphein = writing) is an indispensable diagnostic procedure in obstetrics for the simultaneous (simultaneous) registration and recording of the heartbeat rate of the unborn child and the labor activity in the expectant mother. CTG (cardiotocogram) is used for timely detection of fetal (child) dangerous conditions. The allows to intervene (intervene) early and thus prevent fetal harm.The procedure is used antepartum (before birth) and subpartum (during birth).
Indications (areas of application)
A. Reasons for initial CTG registration as part of prenatal care are:
- Anemia (anemia) of the mother (hemoglobin < 10 g/dL or 6 mmol/L).
- Arrhythmias (cardiac arrhythmia) of the fetus (specifically tachyarrhythmias/combination of arrhythmia/cardiac arrhythmia) and tachycardia/fast heartbeat) diagnosed on ultrasound,
- Bleeding during late pregnancy.
- Blood group incompatibility (blood group incompatibility) with antibody detection.
- Diabetes mellitus
- Doppler findings suspicious (suspect) or pathological/disease (e.g., PI (pulsatility index) in umbilical artery > 90th percentile)
- Drug abuse (e.g., nicotine abuse).
- Hydramnios (abnormally increased amniotic fluid volume; AFI (amniotic fluid index) > 25 cm).
- Hypertension (high blood pressure; ≥ 140/90 mmHg).
- Viral (e.g., TORCH (TORCH complex includes the major infectious diseases or their causative agents that may pose a prenatal risk to the child) including parvovirus B19) and bacterial (AIS) infections.
- Decreased fetal movements
- Maternal (maternal) circulatory instability.
- Multiple pregnancy
- Oligohydramnios (abnormally decreased amniotic fluid; “single pocket” < 2 cm, i.e., when an amniotic fluid niche with a vertical penetration depth < 2 cm is found somewhere).
- Missed due date (> 7 days; see below).
- Thrombophilias (tendency to thrombosis) and collagenoses: collagenoses (group of connective tissue diseases caused by autoimmune processes): systemic lupus erythematosus (SLE), polymyositis (PM) or dermatomyositis (DM), Sjögren’s syndrome (Sj), scleroderma (SSc) and Sharp syndrome (“mixed connective tissue disease”, MCTD).
- Accident with abdominal trauma (injury to abdominal organs) or severe maternal injury.
- Preterm labor/early delivery
- Fetal growth restriction (IUGR, intrauterine growth restriction).
B. Reasons for repeat CTG include the following CTG changes/findings:
- Persistent tachycardia (heart rate > 160/minute).
- Bradycardia (heart rate < 100/minute)
- Decelerations – labor-dependent decrease in the heart rate of the child.
- Hypooscillation, that is, too little variation in heart rate; anoscillation – no variation in heart rate.
- Intrauterine fetal death (IUFT; stillbirth) in previous pregnancy.
- Multiple births
- Suspected placental insufficiency (placental weakness), that is, impairment of fetal metabolism – according to clinical or biochemical findings.
- Tocolysis (drug-induced inhibition of labor).
- Suspected transmission (see below).
- Unclear cardiotocogram findings in suspected preterm labor.
- Uterine hemorrhage (bleeding from the uterus).
The procedure
The device consists of three components: an ultrasound probe (Doppler ultrasound transducer) and a contraction pressure gauge (pressure transducer; tocogram), which are attached to the mother’s abdomen by means of an elastic strap, and an analyzer that processes the signals and records them visibly on a monitor and simultaneously on a paper for documentation.The CTG measures the time interval between two heart sounds of the child and simultaneously records the mother’s contractions via the contraction pressure gauge. From this, the analyzer calculates the heart rate (number of heartbeats per minute) of the unborn baby.Furthermore, there are CTG devices that display movement signals of the baby in a third channel (Kineto-Cradiotocogram = K-CTG). Evaluation scheme – fetal heart rate (K.T. Schneider et al.[S3 Guideline])
| Terminology | Definition |
| Fundamental frequency (SpM) | Mean FHF (fetal/infant heart rate) maintained for at least 5 to 10 minutes in the absence of accelerations (labor-related increases in infant heart rate) or decelerations (labor-related decreases in infant heart rate) in beats per minute (SpM); in fetal immaturity, mean FHF (fetal heart rate) is in the upper scatter range |
| Normal range | 0-150 SpM (beats per minute); at delivery date, ranges from 115 (4th percentile) to 160 beats per minute (96th percentile) (according to Daumer 2007, EL II) |
| Bradycardia |
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| Tachycardia |
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| Bandwidth (variability) | The bandwidth (variability) is the SpM difference of beats per minute) between the highest and lowest fluctuations (fluctuations) in the most prominent minute within the 30-minute recording strip.Fluctuations occur in the fetal (infant) base rate 3 to 5 times per minute.
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| Accelerations | Increase in FHF > 15 SpM or 1⁄2 bandwidth and > 15 seconds.
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| Decelerations | Decelerations Drop in FHF > 15 SpM or > 1⁄2 bandwidth and > 15 seconds.
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CTG allows timely detection of fetal (infant) dangerous conditions. Interpretation of the above parameters:
| Parameter(Assessment) | Fundamental frequency (SpM) | Bandwidth (SpM) | Deceleration | Acceleration |
| Normal |
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| Suspect (suspicious) |
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| Pathological (pathological) |
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Based on the above four criteria, the physician can evaluate a CTG as follows:
- Normal – all four criteria are normal; no action required.
- Suspect – at least one criterion is suspect (suspicious) and all others are normal; need for action: conservative
- Pathological – at least one criterion is pathological (pathologically altered) or two or more criteria are suspect; need for action: conservative or surgical
- Pathological – at least one criterion is pathological or two or more criteria are suspect; need for action: conservative or operative
Further indications
- Deadline overrun and transfer:
- According to a Cochrane analysis based on 34 randomized controlled trials, a significant reduction in perinatal mortality (number of infant deaths in the perinatal period/deaths and deaths up to day 7 postpartum) was shown with a strategy of induction of labor starting at 37. Pregnancy week (SSW) compared with a wait-and-see strategy (22 studies, 18,795 infants): perinatal deaths occurred in 4 cases in the birth induction group and 25 in the wait-and-see group (= relative risk reduction of 69%).
- Inducing labor in low-risk pregnancies (n = 2,760 women) only after 42 SSW resulted in higher perinatal mortality; study was subsequently terminated prematurely.Conclusion: transmission should be considered as early as 41+0 SSW.
Your benefit
With the help of the CTG, your unborn baby is optimally monitored as part of prenatal care.During birth, the CTG shows whether your baby is coping well with the stress of birth and it responds normally to labor.In this way, any disturbances can be detected early and if necessary, timely action can be taken.
