[CG] Outpatient antenatal fetal heart rate monitoring

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There is a recognised need for fetal monitoring for high risk patients. Although there is no clear evidence that antenatal cardiotocography improves perinatal outcome (Grivell et al, 2015) the main purpose of CTG recordings is to identify when there is concern about fetal well-being to enable interventions to be carried out before the fetus is harmed (Beckmann 2014).

The aim of this guideline is to provide a standardised approach to CTG interpretation within the antenatal setting in high risk patients.

Antepartum cardiotocography (CTG) should be considered in women of 26+0 gestation and above. CTG’s carried out before 28 weeks should be performed and interpreted with caution, the decision to do so must be made on an individual basis by a senior obstetrician. The fetal autonomic nervous system is not mature and therefore the patterns of fetal heart rate which may be expected at later gestations are not present. Also there is increased possibility of signal loss and poor quality CTG at earlier gestations (Afors and Chandraharan, 2011). All CTG traces should be peer reviewed by a trained team member. However, all normal CTG traces on fetuses below 32 weeks gestation should also be peer reviewed by an obstetrician (≥ST2) prior to discharging the woman home.

If CTG is of poor quality there should be early recourse to ultrasound location of the fetal heart rate (ideally within 20 minutes).

 

Abdominal examination

A full abdominal examination should be carried out and documented prior to commencing a CTG trace. Ensure the woman has emptied her bladder and is comfortable. Measure fundal height in centimetres, palpate and document the findings. The fetal heart should be auscultated with a Pinard or doptone prior to commencement (Perinatal Institute 2018).

Documentation/ Labelling CTG

All CTG traces  should be labeled with the woman’s name and CHI , the date and time the CTG was commenced , The fetal heart rate on doptone prior to commencing the ctg and the maternal pulse.

Cardiotocography interpretation

When reviewing the cardiotocograph (CTG) trace it is important to assess and document any contractions and all four features of fetal heart rate;

  • Baseline rate
  • Baseline variability
  • Presence or absence of decelerations
  • Presence of accelerations

It is also important to record maternal heart rate. Where there is any difficulty in categorising or interpreting a CTG trace, a review by a senior midwife or obstetrician should be obtained.

The RCOG Green-top Guideline on the management of reduced fetal movements recommends that interpretation of the antenatal CTG fetal heart rate pattern can be assisted by adopting the NICE classification of fetal heart rate features as indicated in their intrapartum care guideline. Therefore, as is the case when classifying intrapartum CTGs, it would seem reasonable to use a structured pro forma to ensure the use of consistent terminology. However, using an intrapartum pro forma is not appropriate as it acknowledges that some decelerations are acceptable in labour, which clearly cannot be the case for antenatal CTGs where there are no contractions.

 

Baseline rate (beats/minute) This is the average fetal heart rate within a ten minute window.

Baseline variability (beats/minute) This refers to the variation of fetal heart rate from one beat to the next. Variability occurs as a result of the interaction between the nervous system, chemoreceptors, baroreceptors and cardiac responsiveness.

 Accelerations are an abrupt increase in the baseline fetal heart rate of greater than 15 bpm for greater than 15 seconds. The presence of fetal heart rate accelerations, even with reduced baseline variability, is generally a sign that the baby is healthy.

Decelerations are an abrupt decrease in the baseline fetal heart rate of greater than 15 bpm for greater than 15 seconds.

Any decelerations on an antenatal CTG should be considered abnormal and prompt medical review.

This pro forma has been adapted from PROMPT training and should be utilised for the classification of CTG traces in non-labouring women only.

Antenatal CTG

Reassuring

Non-reassuring

Baseline rate (bpm)

110-160 Rate:

Less than 109

More than 161

Sinusoidal pattern for 10mins or more

Variability (bpm)

5 bpm or more

Less than 5 bpm for more than 40 minutes

Acceleration

Present

None for 40 minutes

Decelerations

None

Unprovoked deceleration/s

Decelerations related to uterine tightening (not in labour)

Opinion

Normal CTG

(all features reassuring)

Abnormal CTG                       (1 or

more non-reassuring features)

 

Antenatal CTG classification

Normal:       A CTG where all four features fall into the ‘reassuring’ category.

Abnormal: A CTG with any non reassuring features (including any decelerations).

When an abnormal CTG is identified, it should be reviewed by an experienced obstetrician as soon as possible (within 30 minutes) to make a clear individualised action plan

 

Conservative measures

If there are any concerns about the baby’s wellbeing, be aware of the possible underlying causes and start one or more of the following conservative measures based on assessment of the most likely causes: encourage the woman to mobilise or adopt an alternative position ( and to avoid being supine); offer intravenous fluids if the woman is hypotensive or tachycardic.

All cardiotocograph traces must be peer reviewed prior to completion by either a member of midwifery staff or an obstetrician and documented appropriately. If conservative measures fail to resolve an abnormal CTG trace, immediate review by an obstetrician should be sought and a clear and concise plan documented.

 

Preterm Fetal Monitoring

Antepartum cardiotocography should be considered in women of 26+0 weeks gestation and above. Any CTG carried out before 26 weeks should be performed and interpreted with caution. The decision to do so must be based on an individual basis by a consultant obstetrician.

Evidence suggests that the baseline fetal heart rate in preterm fetuses is at the higher end of the normal range for a term fetus for physiological reasons, but that this reverts to the range more consistent with term fetuses as gestation advances. However, any rate more than 160 bpm should be defined as tachycardia across all preterm gestational ages. The baseline variability may be reduced at preterm gestations for physiological reasons. However, at term, fetal heart rate variability is an important clinical indicator of fetal acid base balance and oxygenation of the autonomic nerve centres within the brain (NICE 2015).

Fetal heart rate decelerations are common and normal at very early preterm gestations (26 weeks and less) reflecting immature development of cardioregulatory mechanisms. The presence of shallow or short-lived decelerations in very preterm babies should not be considered necessarily as indicative of hypoxia when all other CTG features are reassuring.

From 32 weeks, baseline fetal heart rate and variability should be similar to that in term fetuses and accelerations with an amplitude of more than 15 beats from the baseline should be present as an indicator of fetal wellbeing. Decelerations can be interpreted as for the term fetus (NICE, 2015).

References

Afors, K. and Chandraharan, E. (2011) Use of Continuous Electronic Fetal Monitoring in a Preterm Fetus: Clinical Dilemmas and Recommendations for Practice. Journal of Pregnancy Volume 2011, Article ID 848794. Available at https://www.hindawi.com/journals/jp/2011/848794/

Beckmann, M. (2014) National German Guideline: Guideline on the use of CTG During Pregnancy and Labour. Geburtsh Frauenheilk.

Grivell RM, Alfirevic Z, Gyte GML, Devane D. Antenatal cardiotocography for fetal assessment (2015). Cochrane Database of Systematic Reviews, Issue 9. Art. No.: CD007863. DOI: 10.1002/14651858.CD007863.pub4.

Kopecky, E, Ryan, M, Barrett et al (2000) Fetal response to maternally administered morphine. American Journal of Obstetrics and Gynaecology. Vol 183-2, August Available at https://ac.els-cdn.com/S0002937800746710/1-s2.0S0002937800746710- main.pdf?_tid=77089bd4-3733-4276-9b11- f5216d79c2f0&acdnat=1521122523_2af4473790c63d9f12e65e3d59fd5cbe

National Institute for Health Care and Excellence (2017) Intrapartum Care (NICE Guideline CG190) Available at: https://www.nice.org.uk/guidance/cg190

National Institute for Health Care and Excellence (2015) Preterm Labour and Birth (NICE Guideline 25) Available at:https://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0080792/pdf/PubMedHealth_PM H00

80792.pdf

Perinatal Institute (2018) Fetal Growth- Fundal Height Measurements. Available online at:

https://www.perinatal.org.uk/FetalGrowth/FundalHeight.aspx

Last reviewed: 11 April 2019

Next review: 01 April 2024

Author(s): Julie Murphy

Approved By: Obstetrics Clinical Governance Group

Document Id: 675