Standard values

The contractions recorder records both the infant’s heart activity and the maternal contractions. Fetal 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, short: bpm).

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, values above 150-160 bpm to tachycardia.

During the examination, the fluctuations of the baseline (oscillations) and whether it changes over longer time intervals (accelerations/decelerations) are also 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. a slowing down of the heart rate, are synonymously called dips.Depending on the size of the drop, synchronicity with contractions and duration of the decelerations, a distinction is made between different stages. If the dips are in principle rather irregular, last only for a short time (less than half a minute) and occur independently of contractions, they can be classified as completely harmless.

Decelerations that occur approximately synchronously with the onset of labor are also considered a good sign and indicate that the baby is responding well to the contractions. However, if the dips occur with a delay or last longer, this may be a sign that the child is not being supplied with sufficient oxygen and that under certain circumstances an induction of labor should be considered. 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 sensation 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.