CTG Flashcards
Antenatal risk factors and indications for CTG
- Diabetes (only uncomplicated diet GDM doesn’t need)
- HTN/PET
- abnormal antenatal CTG
- abnormal Doppler
- FGR
- oligo or polyhydramnios
- prolonged pregnancy ≥ 42 weeks
- multiple pregnancy
- breech
- APH
- PROM
- known fetal abnormality which requires monitoring
- uterine scar
- conditions which constitute a significant
risk of fetal compromise (e.g. cholestasis,
isoimmunisation, substance abuse) - Reduced FM
- BMI ≥ 40
- AMA ≥ 42
- abnormalities of maternal serum screening
associated with an increased risk of poor
perinatal outcomes (e.g. low PAPP-A <0.4MoM
or low PlGF) - abnormal placental cord insertion
Intrapartum indications for CTG
- IOL/synto
- abnormal auscultation or CTG
- regional anaesthesia (e.g. epidural* or spinal)
- bleeding in labour
- maternal pyrexia ≥ 38°C
- Liquor abnormality (mec,blood,absent)
- prolonged first or second stage
- pre-term labour less than 37 completed weeks
- tachysystole, hypertonus hyperstimulation
Intermittent auscultation vs CTG in labour
Relatively small data sizes given that HIE/SB are rare
CTG may increase CS with no perinatal benefit - or may be that the sample size isn’t big enough
Some of this data was based in Ireland where early amniotomy and therefore detection of mec - not the principle of obs care in NZ
Frequency of IA in labour?
1st stage 15-30 mins
2nd stage- every contraction/every 15 mins
Cause of fetal compromise in labour?
placental insufficiency, uterine hyperstimulation, maternal hypotension, cord compression, placental abruption, uterine rupture, fetal sepsis
Features of a normal CTG?
- Baseline rate 110-160 bpm.
- Baseline variability of 6-25 bpm.
- Accelerations 15bpm for 15 seconds.
- No decelerations.
Features unlikely to be associated with fetal
compromise when occurring in isolation:
- Baseline rate 100-109 bpm.
- Reduced or reducing baseline variability 3-5bpm.
- Absence of accelerations.
- Early decelerations.
- Variable decelerations without complicating features.
Which features may be associated with significant fetal
compromise and require further action?
- Baseline fetal tachycardia >160 bpm.
- Rising baseline fetal heart rate (including where it remains within normal range).
- Complicated variable decelerations.
- Late decelerations.
- Prolonged decelerations (a fall in the baseline fetal heart rate for more than 90 seconds and up to 5 minutes).
Which features are likely to be associated with significant fetal compromise and require immediate management, which may include urgent delivery:
- Bradycardia (a fall in the baseline fetal heart rate for more than 5
minutes) . - Absent baseline variability <3bpm.
- Sinusoidal pattern.
- Complicated variable decelerations with reduced or absent baseline variability.
- Late decelerations with reduced or absent baseline variability.
Tachysystole?
more than five active labour contractions in ten minutes, without fetal heart rate abnormalities
Hypertonus?
contractions lasting longer than two minutes in duration or contractions occurring within 60 seconds of
each other, without fetal heart rate abnormalities
Hyperstimulation?
Excessive uterine activity, (either tachysystole or uterine hypertonus) with fetal heart rate abnormalities.
Causes of tachysystole?
Induction of labour
Abruption
Infection
Risks of hyperstimulation?
Fetal hypoxia/distress
Uterine rupture
AFE
Tocolytic regimens?
- salbutamol, 100 micrograms intravenously;
- terbutaline, 250 micrograms intravenously or
subcutaneously or - GTN spray, 400 micrograms sublingually.
Contraindications to FBS:
- Evidence of serious, sustained fetal compromise.
- Risk of fetal bleeding disorders (e.g. fetal thrombocytopenia, haemophilia).
- Non-vertex presentation.
- Maternal infection* (e.g. HIV, hepatitis B, hepatitis C, active primary herpes and suspected fetal sepsis). *Group B Streptococcus carrier status does not preclude FBS.
- Gestation <34/40
Paper speed of CTG?
1cm/minute
When should cord gases be taken?
- Apgar score < 4 at 1 minute.
- Apgar score < 7 at 5 minutes.
- Fetal scalp sampling performed in labour.
- Operative delivery undertaken for fetal compromise.
Baseline rate definition
The mean level of the fetal heart rate when this is stable, excluding accelerations and decelerations and contractions. It is typically 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 progressive rise in the baseline is important as well as the absolute values
Variability
The minor fluctuations around the baseline FHR. It is assessed by estimating the difference in beats per minute between the highest peak and lowest trough of fluctuation in one minute segments of the trace between contractions.
6-25 normal
3-5 reduced
<3 absent
>25 increased
Accelerations
Transient increases in FHR of 15 bpm or more above the baseline and lasting 15 seconds at the baseline. Accelerations in the preterm fetus may be of lesser amplitude and shorter duration.
The significance of no accelerations on an otherwise normal CTG is unclear
Early decelerations
Uniform, repetitive decrease of FHR with slow onset early in the contraction and slow return to baseline by the end of the contraction.
Variable decelerations
Repetitive or intermittent decreasing of FHR with rapid onset and recovery.
Time relationships with contraction cycle may be variable but most commonly occur
simultaneously with contractions
Complicated decelerations
The following additional features increase the likelihood of fetal hypoxia:
- Rising baseline rate or fetal tachycardia.
- Reducing baseline variability.
- Slow return to baseline FHR after the end of the contraction.
- Large amplitude (by 60 bpm or to 60 bpm) and/or long duration (60 seconds).
- Presence of smooth post deceleration overshoots (temporary smooth increase in FHR above baseline).
- Biphasic decelerations
If associated with reduced variability and rising BR likely signifies the fetus is losing its ability to compensate for ongoing hypoxia or mechanical stress
Prolonged decelerations
A fall in the baseline fetal heart rate for more than 90 seconds and up to 5 minutes
Bradycardia
A fall in the baseline fetal heart rate for more than 5 minutes
Late decelerations
Uniform, repetitive decreasing of FHR with, usually, slow 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 of <15 bpm.
Why does the FHR drop in response to hypoxia?
Adults can respond to reduced O2 by increasing RR and depth of inspiration
Fetuses are unable to do this, therefore to protect their myocardium they decrease their HR
This is a response to hypoxic or mechanical stress
Features of typical/uncomplicated decelerations?
a drop of <60pm
duration of <60s
Shouldering
Secondary to mechanical compression of the cord
Types of intrapartum hypoxia
- Acute
- Subacute
- Gradually evolving
- Chronic
How quickly does the fetal pH fall in response to acute hypoxia?
0.01 per minute
Results in drop of 0.15 over 15 minutes (e.g. 7.2->7.05)
Management of acute hypoxia
- Sudden drop in FHR for >3 minutes
Mx:
- Exclude 3 major ‘accidents’: rupture, cord prolapse, abruption
- Correct iatrogenic causes: e.g. hyperstimulation/hypotension: IVF, stop synto and give tocolysis
- Change maternal position
