CTG definitions

ean 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. 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 values

Normal Baseline FHR
110-160 bpm

Abnormal bradycardia
<100 bpm

Abnormal tachycardia
>180 bpm

Baseline variability
The minor fluctuations in baseline FHR occurring 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 or equal to 5 bpm between contractions

Non-reassuring baseline variability
Less than 5 bpm for 40 minutes or more but less than 90 minutes

Abnormal baseline variability
Less than 5 bpm for 90 minutes or more

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

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

Late decelerations
Uniform, repetitive, periodic slowing of FHR with onset mid to end of the contraction and nadir more than 20 seconds after the peak of the contraction and ending after the contraction. In the presence of a non-accelerative trace with baseline variability < 5 bpm, the definition would include decelerations < 15 bpm

Variable decelerations
Variable, intermittent periodic slowing of FHR with rapid onset and recovery. Time relationships with contraction cycle are variable and they may occur in isolation. Sometimes they resemble other types of deceleration patterns in timing and shape

Atypical variable decelerations
Variable decelerations with any of the following additional components: i. loss of primary or secondary rise in baseline rate, ii. slow return to baseline FHR after the end of the contraction. iii. prolonged secondary rise in baseline rate, iv. biphasic deceleration, v. loss of variability during deceleration, vi. continuation of baseline rate at lower level.

Prolonged deceleration
An abrupt decrease in FHR to levels below the baseline that lasts at least 60-90 seconds. These decelerations become pathological if they cross two contractions, i.e. greater than 3 minutes

Sinusoidal pattern
a regular oscillation of the baseline long-term variability resembling a sine wave. This smooth, undulating pattern, lasting at least 10 minutes, has a relatively fixed