In the third trimester of pregnancy, the mother's belly is already nicely rounded. Now the birth is fast approaching. From around the 30th week of pregnancy, many pregnant women now also become acquainted with the so-called CTG - i.e. the labour monitor - during check-ups. Most are happy about this because it allows them to listen to the heartbeat of their unborn child.
The abbreviation CTG stands for cardiotocography. The term is a combination of the words "cardio" for heart, "toko" for contraction and "graphie" for recording and already reveals the function of the device. As a so-called cardiotocograph, the device makes the heartbeat of your unborn baby audible and records it. At the same time, it also displays your labour activity. It then records all the values as curves on a paper strip, which the device continuously "spits out". Some devices now also store the results purely digitally. By the way: Your midwife can also carry out a CTG as part of your antenatal check-ups.
This non-invasive diagnostic procedure was invented by the German gynaecologist and obstetrician Konrad Hammacher (1928 to 2001) in 1964, for which the technology-interested physician was even awarded the Order of Merit of the Federal Republic of Germany. His innovative procedure was able to significantly reduce the mortality rate for babies during pregnancy and birth. The purpose of the CTG is to monitor your baby's oxygen supply and to register whether changes in its heart rate are related to the contractions. In short: a CTG is used to check whether your baby is doing well.
Until this method was invented, the heartbeat of the unborn child was monitored solely with the wooden Pinard stethoscope, the well-known "midwife's ear trumpet". This can also be used to determine how the unborn child is doing. In addition to all the modern technology, this "classic" in everyday midwifery care is still used reliably by many colleagues today.
When is a CTG written?
A CTG can be recorded during pregnancy and during labour. The Maternity guidelines for prenatal care, however, only provide for this check-up for certain indications. These include, for example, premature labour, placental insufficiency or gestational diabetes, as well as multiple pregnancies. A CTG is also taken every time a missed appointment is scheduled.
The reason for this restriction is that Studies show that there is no positive benefit to taking a CTG in a healthy pregnant woman. On the contrary, recent years have shown that taking a CTG leads to countless unnecessary interventions. We now know that the benefits of this measurement method have been greatly overestimated for many years.
However, the practice is different: In most gynaecological practices, however, a CTG is still routinely taken around the 30th week of pregnancy at the antenatal appointment. You will then be connected to the device for around 20 - 30 minutes.
The baby's heartbeat is also checked regularly during labour. However, studies have also shown that the routine use of a labour monitor in healthy pregnant women has no positive benefit. It has also been shown that this use leads to more interventions in the birth process and does not result in a safer birth for mother and child in healthy pregnant women (low risk).
A CTG should therefore only be taken during labour if there is a medical reason to do so. This may be because the mother and baby have special medical findings, meaning that the health parameters need to be monitored particularly closely. In principle, however, the CTG is also used when medical interventions, such as a Induction of labour or a Peridural anaesthesia (PDA), make intensive medical monitoring necessary.
In many clinics, however, a CTG is recorded for all women during labour. The reason for this is often a lack of staff, which does not allow the midwives to use other methods. During the birth in the maternity clinic, the CTG device is often connected for 10 to 20 minutes about once an hour during regular contractions. During the last phase of labour, the exit phase, you may also remain permanently connected. Your baby is now in the most stressful phase of labour.
Modern cardiotocographs also work wirelessly so that the woman giving birth can move around freely.
Regardless of the time - don't be shy and don't hesitate to ask if anything is unclear during the CTG or if you are worried about something. Even if the doctor is concerned: Always follow up and ask them to explain what's going on.
How does the CTG work?
Put simply, the cardiac labour recorder converts ultrasound signals into visible curves. For this purpose, there is an ultrasound probe that is attached to the pregnant woman's abdomen together with a contraction pressure gauge using an elasticated belt. The ultrasound probe continuously transmits ultrasound waves that are reflected by the baby's heart. This measures the time between two heartbeats of the baby. The "response signals" are transmitted to an analyser. This then calculates how often the baby's heart beats per minute and displays the result as a curve.
The contraction pressure gauge in turn determines the length and frequency of the contractions that build up each time the uterus contracts. The values appear as a second curve below the first on the printed paper strip. From the interaction of both curves, conclusions can then be drawn about how the baby's heart rate behaves in relation to the mother's contractions. However, it is not always easy to draw conclusions about how the child is actually doing. To do this, however, it is not enough to look at a short section of the results; the entire curve is always analysed. Other parameters are added to this. These include, for example, the baby's movement pattern in the abdomen.
However, the CTG cannot be used to reliably and objectively determine how strong the contractions are. This is because the pressure dissipation depends on the exact position of the contractions recorder and the thickness of the abdominal wall, which lies over the uterus and reduces the pressure dissipation from the uterus.
My tip: orientate yourself on how you feel during contractions and don't be confused by the height of the contraction curve on the paper strip.
By the way: Some modern CTG devices also record the baby's movements in the mother's abdomen. This is known as a kineto-cardiotocograph, abbreviated to K-CTG.
What do the CTG curves reveal?
The two curves that the analyser records are unevenly jagged upwards and downwards. A mum - a chartered accountant by profession - once said to me with a wink: "You know, Katharina, it kind of reminds me of share price movements." It's a funny comparison - but still: just like the stock market, minor irregularities in the CTG don't automatically mean that there is cause for concern.
As mentioned, the CTG curves include the so-called basic frequency for the baby's heartbeat. This should average between 110 and 160 beats per minute. However, this basic frequency does not result from an equal number of heartbeats per minute, but has a fluctuation range of over 5 to 25 beats per minute. If the baby is actively dreaming or moving in the womb, its heart can also beat faster.
In connection with the labour activity of the exit phase, in which the baby has to squirm through the narrow pelvis, it can also happen that the heart sounds briefly drop below the basic frequency.
When the uterus contracts during a contraction, less blood (and therefore less oxygen) reaches the baby from the placenta for this moment. At the same time, the labour pressure acts on the baby's head. Baby's heart then beats more slowly for a moment, but returns to normal as soon as the contraction subsides.
However, if the heart rate does not return to normal, the midwife or doctor will take another closer look. During labour, a sudden or prolonged drop in the baby's heart rate may indicate that the birth is too strenuous for your baby.
One speaks of so-called Decelerationif the baby's heart rate is reduced by at least 15 beats per minute for 10 seconds to three minutes. If, on the other hand, the baby's heart rate increases by 10 to 15 beats per minute for 15 seconds to 10 minutes, this is a so-called Acceleration before. In order to judge how the baby is really doing, however, the frequency of these "upward outliers" as well as the "downward outliers" is also important.
Every experienced midwife and gynaecologist is able to analyse a CTG. To do this, it is analysed according to a certain scheme - a so-called score (Fischer score or FIGO score). This allows the values to be categorised. Sometimes certain circumstances, such as the mother's age or medication she is taking, also play a role in their evaluation. If the results are abnormal, certain further tests are then arranged.
My tip: Anyone who has a CTG appointment with the midwife or at the gynaecologist's practice should really drink enough beforehand. The fluid stabilises the pregnant woman's circulation and stimulates the kidneys and metabolism in general. These are good prerequisites for unadulterated CTG results.
CTG: Safe for mother and child?
Some mothers have already asked me whether cardiotocography could have a negative effect on their unborn child. If used correctly from a medical point of view, you don't need to worry. It is important that the CTG is only used when it fulfils a medical purpose. This means you can be sure that neither the ultrasound waves nor interpretation errors can harm your baby. Ultimately, this ultrasound exposure of the heart contraction recorder, as with the Ultrasound examinations during your screening appointments, to a sound exposure for which no damage has been proven and which not are affected by the ban on the use of ultrasound waves during pregnancy by the Federal Office for Radiation Protection (Ordinance on protection against the harmful effects of non-ionising radiation when used on humansn).
A word about foetal dopplers for private use
There are now many devices available for parents to rent or buy that allow them to hear and measure their unborn child's heart rate at home. These are known as fetal dopplers. They also send out ultrasound waves and analyse the sound waves that come back. However, these must be assessed differently. This is because they are not used by medically trained people and not for the purpose of a necessary medical examination. They therefore fall under the prohibition of use in the Radiation Protection Ordinance. This also makes it clear that the effects of ultrasound cannot be definitively determined. This applies in particular to diagnostic methods whose effects cannot be investigated because everyone can use them according to their own needs.
Many expectant mothers and fathers love listening to their child's heartbeat and find this technology so wonderful that the use of "home devices" has become really fashionable. With some models, the foetus's heartbeat is said to be audible from around the 10th week of pregnancy. The manufacturers promise that this gives parents a good feeling of security, especially in the first trimester, when there is still uncertainty as to whether the pregnancy will continue.
As much as I, as a midwife, understand the appeal for pregnant women to use these devices, I strongly advise against it.
What is the problem with the foetal Doppler for home use?
- Firstly, parents may not find the foetus's heartbeat at all - or accidentally hear the wrong pulse, namely the mother's lower one. In both cases, the reaction is often panic. And that is not at all good for a pregnant woman or her child!
- Secondly, there are sometimes technical reasons why these home devices do not reliably display your baby's heartbeat. This also causes more stress than benefit for parents.
- Thirdly, parents who are not medically trained have to interpret the instructions for use themselves to see whether the results are OK. This often leads to false conclusions and, as a result, either to great uncertainty or to a supposed sense of security and reduced vigilance.
- And fourthly, a dependency on the devices can develop, as described above, which puts parents under chronic tension and forces them to use the device again and again for reassurance.
These are four good reasons to take a critical view of the use of home appliances.
My tip: During pregnancy, trust your body to ensure that your child develops well. If you are unsure whether the baby in your womb is doing well, don't hesitate to seek advice from your midwife or doctor. Then you are always in competent hands and on the safe side!
