Last edited 12/2022 and last reviewed 01/2023
Cardiotocography provides a simultaneous record of the foetal heart rate and magnitude of uterine contractions.
The foetal heart rate is recorded in the first instance using a abdominal doppler ultrasound sensor. If this proves inefficient then a foetal scalp electrode may be attached during labour.
Maternal contractions are recorded using an abdominal wall pressure sensor. The recorded strength of a contraction is only an estimate as it is altered with position, abdominal wall obesity. However the length of a contraction does provide useful information in the interpretation of foetal heart rate abnormalities.
The fetal heart increases with increasing gestational age. There is an increase in heart rate variability with increasing maternal age.
NICE suggest that (1):
- perform an initial assessment of antenatal risk factors for fetal compromise at the onset of labour to determine whether intermittent auscultation or cardiotocography (CTG) is offered as the initial method of fetal heart rate monitoring
- explain to women that if there are no identified risk factors for fetal compromise:
- there is a risk of increased interventions with continuous CTG monitoring compared with intermittent auscultation, which may outweigh the benefits and
- advice she is given by her midwife or obstetrician on the method of fetal heart rate monitoring will take into account the whole clinical picture
- discuss with the woman and her birth companion(s) the reasons for offering continuous CTG monitoring, and explain that:
- a combination of antenatal risk factors, intrapartum risk factors and continuous CTG monitoring are used to evaluate the baby's condition in labour
- continuous CTG monitoring is used to monitor the baby's heart rate and the labour contractions
- it may restrict her mobility and the option to labour in water
- a normal CTG trace indicates that the baby is coping well with labour
- changes to the baby's heart rate pattern during labour are common and do not necessarily cause concern, however they may represent developing fetal compromise so maintaining continuous CTG monitoring is advised if these occur
- if the CTG trace changes or is not normal there will be less certainty about the condition of the baby and so maintaining continuous CTG monitoring is advised, in conjunction with a full assessment including checks for developing intrapartum risk factors such as the presence of meconium, sepsis and slow progress in labour
- advice about her care during labour and birth will be based on an assessment of several factors, including her preferences, her condition and the condition of her baby, as well as the findings from the CTG
CTG vs. CTG plus PR interval analysis