5 Assessing fetal heart rate

27. How should you monitor the fetal heart rate?

Because uterine contractions may decrease the maternal blood flow to the placenta, and thereby cause a reduced supply of oxygen to the fetus, it is essential that the fetal heart rate is monitored during labour. In practice, this means that the fetal heart rate must be checked before uterine contractions to determine the fetal heart rate between contractions, then again during and after the contraction. A comment on the fetal heart rate, without knowing what happens before, during and after contractions, is of very limited value.

The fetal heart rate must be assessed before, during, and after a contraction.

The fetal heart rate assessed before, during and after a contraction is called the fetal heart rate pattern. This provides important information on the fetal condition.

28. How often should you routinely monitor the fetal heart rate?

Low-risk women who have had a normal pregnancy with normal observations on admission:

1. Two hourly during the latent phase of labour
2. Half-hourly during the active phase of labour

29. Which women are considered to have a high risk of fetal distress?

The following women would be regarded as high risk:

1. Women with medical problems during pregnancy, especially pre-eclampsia, chronic hypertension, antepartum bleeding and diabetes
2. Women who smoke
3. Women with slow fetal growth (growth restriction) or oligohydramnios (little amniotic fluid)
4. Women with clinical signs indicating chorioamnionitis (fever, abdominal tenderness and offensive vaginal discharge)
5. Women with meconium-stained amniotic fluid
6. Women with poor progress in labour

If possible, these high-risk women should have continuous electronic fetal heart rate monitoring during labour with a CTG. If this is not possible, the fetal heart rate should be observed more frequently with a fetal monitor.

30. How often must the fetal heart rate be monitored if there is a high risk of fetal distress?

When using a fetal monitor:

1. Hourly during the latent phase of labour
2. Half-hourly during the active phase of labour
3. At least every 15 minutes if fetal distress is suspected
4. Directly after every bout of maternal pushing during the second stage of labour

31. What features of the fetal heart rate pattern should you always assess during labour?

There are two features that should always be assessed:

1. The baseline fetal heart rate.
2. The presence or absence of decelerations: If present, the relation of the deceleration to the contraction must be determined. It is very important to compare the timing of the contraction to the timing of the deceleration.

The baseline fetal heart rate and the presence or absence of decelerations must always be assessed and recorded.

32. What is the normal baseline fetal heart rate?

The baseline fetal heart rate is the fetal heart rate between uterine or just before contractions. The baseline fetal heart rate is normally between 110 and 160 beats per minute.

33. What is a deceleration?

This is a temporary slowing down of the fetal heart rate. Decelerations are almost always related to contractions and can be detected with a fetal monitor.

Note

It is the timing of the deceleration relative to the contraction rather than the degree of slowing of the fetal heart rate that is important.

34. How do decelerations relate to the timing of contractions?

1. Decelerations that occur only during a contraction (i.e. early decelerations)
2. Decelerations that occur during and after every contraction (i.e. late decelerations)
3. Decelerations that have no fixed relation to contractions (i.e. variable decelerations).

35. What is an acceleration?

An acceleration is a speeding up of the heart rate. Accelerations are normal and do not indicate fetal distress. During pregnancy they usually occur with fetal movements. During labour, accelarations usually occur during a contraction.

36. What fetal heart rate patterns can easily be recognised with a fetal monitor?

1. Normal
2. Baseline tachycardia
3. Baseline bradycardia
4. Early deceleration
5. Late deceleration

Usually these fetal heart rate patterns can be easily recognised with a fetal monitor. However, variable decelerations are more difficult to recognise. It is common to get a combination of patterns, e.g. a baseline bradycardia with late decelerations. It is also common to get one pattern changing to another pattern with time, e.g. early decelerations becoming late decelerations.

CTG tracings can be used to learn how to recognise different fetal heart rate patterns. This knowledge is very useful when using a fetal monitor.