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KTG is a method created by combining fetal cardiography and tokography. During cardiography, the fetal heart rate is recorded, and during tocography – the contractile activity of the uterine muscle. The combination of these two methods makes it possible to fully supervise the fetus – especially during the delivery period.
CTG machine – the cardiotocograph has two heads that are attached to the pregnant belly: for the tokographic measurement – in the area of the uterine fundus, for the cardiographic measurement of the fetal heart – in the area where it is best audible.
The fetal heart rate ranges from 120 to 160 beats per minute – so it is about twice as fast as the adult human heart rate. Exceeding the normal range by more than 20 beats per minute up is severe tachycardiaand down – heavy bradycardia. Especially the latter case should raise concerns about the condition of the fetus.
Sudden severe bradycardia, i.e. a slowed down of the fetal heart rate, may result from acute hypoxia, e.g. as a result of compression of the inferior vena cava by the uterus when the pregnant woman is supine. Therefore yes it is important that the expectant mother sleep on her left side, and not on her back.
Other reasons acute bradycardia is increased contraction of the uterine muscle, premature detachment of a properly seated placenta, compression of the umbilical cord, its loop around a part of the baby’s body, or jamming between the uterine wall and the fetal head during delivery. Transient bradycardia sometimes occurs physiologically in the second stage of labor during the birth of the head. Pressing the latter in the birth canal causes a nervous reflex resulting in a slowdown of the fetal heart rate. However, in the event of acute bradycardia during delivery, not related to head birth, the pregnancy should be terminated immediately by caesarean section.
Chronic bradycardia most often accompanies fetal heart defects. Its presence during CTG examination is an indication for in-depth cardiological diagnostics in the fetus.
The most common cause tachycardia there are infections, including intra-aquatic infections, as well as the mother’s fever, some medications and low fetal maturity.
When analyzing the CTG recording, one should also pay attention to oscillations, i.e. slight fluctuations in the fetal heart rate that occur over a short period of time. There are 4 types of oscillation: silent (0-5 bpm), narrow (5-10 bpm), undulating (correct, 10-25 bpm) and jumping (more than 25 bpm). It should be remembered that the fetus also has periods of sleep and wake, which are reflected in the CTG traces. During sleep, the oscillation may narrow.
What worries obstetricians the most are the so-called decelerations – layoffs. They involve a temporary reduction in the fetal heart rate of at least 15 beats / min. in relation to the basic activity, lasting for a minimum of 10 seconds. Decelerations can be early – associated with an increase in intracranial pressure in the fetus and the (physiological) stimulation of the vagus nerve, or late, caused by fetal hypoxia due to various reasons. The prognosis for late decelerations depends on what caused them and what steps were taken in the delivery room to complete delivery. The so-called variable decelerations not directly related to fetal hypoxia. In terms of prognosis, they may turn out to be much worse than late decelerations.