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Cardiotocography (sometimes known as electronic fetal monitoring), records changes in the fetal heart rate and their temporal relationship to uterine contractions. The aim is to identify babies who may be short of oxygen (hypoxic), so additional assessments of fetal well-being may be used, or the baby delivered by caesarean section or instrumental vaginal birth. The objective is to reduce perinatal mortality and morbidity and any possible long-term complications of reduced oxygen supply occurring in labour.
Figure 1. A Normal CTG. The rate is 130 beats per minute. FHR variability is normal. There are accelerations and no decelerations.
There is a gradual fall in baseline with advancing gestational age up to 30 weeks. The female has a significantly faster heart rate than the male.9901 From the limited evidence relating isolated baseline abnormalities to robust neonatal outcomes, it appears that the normal ranges for a term fetus lies between 110 bpm and 160 bpm. In the absence of infection, an uncomplicated baseline of 110?119 bpm or 161?179 bpm are probably not associated with adverse neonatal outcome, although in the presence of other non-reassuring FHR features or if there has been a rise in baseline, these baseline fetal heart rates should be investigated further. RCOG Baseline Fetal Heart Rate: The mean level of the FHR when this is stable, excluding accelerations and decelerations. It is determined over a time period of 5 or 10 minutes and expressed in bpm.11 Preterm fetuses tend to have values towards the upper end of this range. A trend to a progressive rise in the baseline is important as well as the absolute.Normal Baseline: FHR 110?160 bpmBaseline variability: The minor fluctuations in baseline FHR occuring at three to five cycles per minute. It is measured by estimating the difference in beats per minute between the highest peak and lowest trough of fluctuation in a one-minute segment of the trace. Normal baseline variability: Greater than or equal to 5 bpm between contractions variability.
Fetal Heart Rate Accelerations
Accelerations: Transient increases in FHR of 15 bpm or more and lasting 15 seconds or more. The significance of no accelerations on an otherwise normal CTG is unclear.
The presence of accelerations of the fetal heart rate during labour
proved to be an excellent indicator of subsequent good fetal outcome.7901
Three accelerations indicate fetal well-being as much as any higher
number of accelerations per 30 minutes.8201
Decelerations: Transient episodes of slowing of FHR below the baseline level of more than 15 bpm and lasting 15 seconds or more. Early decelerations: Uniform, repetitive, periodic slowing of FHR with onset early in the contraction and return to baseline at the end of the contraction.
Early Decelerations. The trough of the deceleration is at the height of the contraction. There are uniform, repetitive, periodic slowing of FHR with onset early in the contraction and return to baseline at the end of the contraction. They relate to descent of the head in the maternal pelvis. Early decelerations are not associated with reduced 5-minute Apgar scores8001 or metabolic acidosis.9901
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