Introduction
A cardiotocogram, or CTG for short, is used to measure fetal heart activity and maternal contractions. Overall, this procedure is used to monitor late pregnancy or the birth itself. The heart activity of the unborn child is measured using Doppler ultrasound and recorded as a heart rate.
The mother’s contractions are measured using a pressure sensor which registers the change in abdominal circumference during a contraction. However, depending on the physical constitution of the pregnant woman, the pressure measurement may vary and not provide very accurate values. Therefore, in addition to the actual measurement, the subjective feeling about the perception of the contractions by the pregnant woman is also important.
It is best for the expectant mother to lie on her side or on her back for the duration of the examination. Two straps are usually placed around her abdomen to hold the respective measuring sensors on the abdominal wall. Usually the sensors are connected to the actual device for recording via a cable.
There, the measured data can be printed on paper strips. With modern devices, data transmission is also possible via radio, so that the woman can move freely during the examination. By measuring the child’s heartbeat, the cardiotocogram also provides information about the oxygen supply of the unborn child, which is essential for the physical development. If, for example, the heart rate drops, this should be interpreted as a direct sign of a reduced oxygen supply and should be corrected as quickly as possible in order not to endanger the health of the unborn child.
Standard values
Childhood heart activity is expressed as heart rate in beats per minute. As a rule, it should be between 110 and 150 beats per minute (also: beats per minute, or bpm for short). Towards the time of birth it can even increase a little, usually up to 160 bpm.
The basic frequency corresponds approximately to the resting pulse of the adult and is called the baseline for the contractions recorder. Values below 110 bpm medically correspond to bradycardia (a slowed heartbeat), values above 150-160 bpm to tachycardia (a fast heartbeat). If such a condition lasts longer, the cause should definitely be clarified further.
In order to determine further standard values for the CTG examination, it is first necessary to examine the individual changes in the child’s baseline more closely. During the examination, not only the baseline itself but also its fluctuations (oscillations) and whether it changes over a longer period of time (accelerations/decelerations) are assessed. The heart rate is not always constant even in unborn babies, but should not deviate from an average frequency by more than about 15-20 bpm.
On the CTG curve, this phenomenon manifests itself as a curve with small spikes. On the other hand, if the heart rate were always constant at one value, you would have a straight line. Normally, such oscillations occur especially with changes in the child’s position.
On average, about three to five such oscillations should be measured per minute of CTG recording. A prolonged increase in the basic frequency is called acceleration in CTG, whereas a slowdown is called deceleration. It is important that the baseline change is more than 15 bpm and lasts longer than 15 seconds.
Accelerations are also a sign of the child’s vitality and healthy activity. Normally, there should be about 2 accelerations per 30 minutes of CTG measurement. Decelerations, i.e. slowing down of the heart rate, are synonymously called dips.
Depending on the size of the dip, synchronicity with contractions and the duration of the decelerations, different stages are distinguished. Some of them are more likely to be harmless, while others may be signs of a lack of supply. The activity of the contractions is measured as tension on the abdominal wall, which usually changes during contractions. However, depending on the physical constitution of the mother, this measurement is not always very accurate, which is why the subjective perception of the woman is also very important for the assessment. On the CTG recording, the size, regularity and duration of the contractions can then be further assessed.
