Fetal surveillance in labour Flashcards
What proportion of cerebral palsy is estimated to be due to intrapartum hypoxia?
10%
What causes intrapartum hypoxia?
Blood supply to the placental pool is restricted, with contractions (especially in the second stage) placing a physiological strain on the fetus
Ability to withstand stress dependent on fetal reserve; may cope in antenatal period but have no extra reserve and decompensate in labour
What are 2 options for intrapartum surveillance?
- Intermittent auscultation (IA)
- Continuous CTG, also known as electronic fetal monitoring (EFM)
When should CTG be performed in the intrapartum period?
not advised routinely for low-risk women in suspected or established labour; should be performed is there is difficulty or some abnormality of the FHR on auscultation
If CTG is performed due to FHR abnormality on auscultation, when can it be discontinued?
if CTG normal for 20 minutes
What monitoring of the fetal heart rate should be performed in labour?
- on admission in labour, FHR should be auscultated for 1 min and entered as a single rate. Maternal heart rate should be palpated simultaneously to distinguish FHR as distinctly different
- if no risk factors, intermittent auscultation for full minute after a contraction
- at least every 15 min in first stage
- every 5 min or after every other contraction in the second stage
- any accelerations or decelerations that are auscultated should be recorded
- if fetal death suspected, US should be performed
What are 9 antenatal maternal risk factors that should prompt recommendation of electronic fetal monitoring (continuous CTG) in labour?
- Previous caesarean section
- Cardiac problems
- Pre-eclampsia
- Prolonged pregnnacy (>42 weeks)
- Prelabour rupture of membranes (>24h)
- Induction of labour
- Diabetes
- Antepartum haemorrhage
- Other significant maternal medical conditions
What are 7 fetal antenatal risk factors that should prompt recommendation of EFM (continuous CTG) in labour?
- IUGR
- Prematurity
- Oligohydramnios
- Abnormal doppler velocimetry
- Multiple pregnancy
- Meconium-stained liquor
- Breech presentation
What are 7 intrapartum risks requiring EFM (continuous CTG)?
- Oxytocin augmentation
- Epidural analgesia
- Intrapartum vaginal bleeding
- Pyrexia >37.5oC
- Fresh meconium staining of liquor
- Abnormal FHR on intermittent auscultation
- Prolonged labour
What are 2 disadvantages/effects of electronic fetal monitoring?
- increased intervention and operative delivery rates
- no marked decrease in cerebral palsy
What are 5 reasons why EFM is likely to result in increased intervention and no marked decrease in cerebral palsy?
- CTG is not specific enough in detecting fetal hypoxia
- Failure to consider the clinical situation
- Poor interpretation
- Delay in taking action
- Intrapartum hypoxia as a cause of CP is rare
What is are 2 that can be used alongisde EFM to increase specificity?
- fetal scalp blood sampling (FBS) - but recent studies questino its value
- ECG ST waveform analysis (STAN) - improves positive predictive value of CTG
What is the definition of baseline rate when referring to cardiotocography?
mean level of the FHR when this is stable, and after exclusion of accelerations and decelerations
What is the definition of baseline variability in reference to CTG?
degree to which the baseline varies, i.e. bandwidth of baseline after exclusion of accelerations and decelerations. Variability of 5–25 beats/min is defined as normal, 0–5 beats/min as reduced, and >25 beats/min as saltatory.
What baseline variability of the CTG is considered 1. normal 2. reduced and 3. saltatory?
- Normal: 5-25 beats/min
- Reduced: 0-5
- Saltatory: >25
What is the definition of acceleration in reference to CTG?
a transient rise in FHR from a steady baseline rate by at least 15 beats lasting for 15s or more
What is the definition of deceleration in reference to CTG?
a reduction in the baseline of 15 beats or more for more than 15s.
What does the CTG shown show?
several accelerations and normal baseline variability and no decelerations with contractions suggestive of healthy fetus
What are the 2 most useful features in assessing fetal wellbeing from CTG?
- Normal variability: reflection of autonomic nervous system, sympathetic and parasympathetic
- Presence of accelerations: somatic nervous system
When should you always be concerned about a CTG?
if you cannot identify the baseline rate
What are 7 causes of decreased baseline variability in a CTG?
- Fetal hypoxia
- Fetal sleep cycle (should be for <40 and maximally 90min)
- Fetal malformation (CNS or cardiac) or arrhythmias
- Administration of drugs
- Severe prematurity
- Fetal heart block
- Fetal anomalies
What are 7 examples of drugs which, when administered, can cause decreased baseline variability of the CTG?
- methyldopa
- magnesium sulphate
- narcotic analgesics
- corticosteroids
- transquilizers
- barbiturates
- general anaesthesia
What are 2 examples of types of CTG abnormalities?
- Abnormalities in baseline rate
- Decelerations
What is the definition of a bradycardia based on CTG?
baseline FHR of less than 110 beats/min
What are 2 groups that bradycardia based on the CTG can be classified into?
- 100-110 beats/min: moderate baseline bradycardia, on its own not associated with fetal compromise if baseline variability normal and accelerations present
- <100 beats/min: should raise possibility of hypoxia or other pathology
What should you be especially aware of if FHR is below 110?
maternal heart rate being recorded as the FHR
What is the definition of tachycardia based on CTG?
baseline FHR >160 beats/min
What are 4 things which tachycardia in the fetus can be associated with?
- Maternal pyrexia
- Maternal tachycardia
- Prematurity
- Fetal acidosis
What are 2 groups that fetal tachycardia can be classed into?
- 160-180 beats/min: moderate baseline tachycardia, on its own likely not indicative of hypoxia if baseline variability normal and accelerations present
- >180 beats/min should always raise suspicion of underlying pathology
What are 2 types of decelerations on the CTG?
- Early decelerations
- Late decelerations
What is the definition of early decelerations?
the peak of the deceleration coincides with the peak of the contraction
this is related to head compression and therefore should only be seen in late first stage or active second stage of labour
What is the definition of late decelerations?
have at least a 20s time lag between the peak of the contraction and the nadir of the deceleration
What in particular may decelerations be suggestive of and what particularly supports this?
Acidosis; especially if accompanied by tachycardia and reduced baseline variability
What do shallow, late decelerations in the presence of reduced baseline variability on a non-reactive trace suggest?
should be of particular concern - may be preterminal, especially if associated clinical risks e.g. IUGR, absent FM, bleeding, infection, prolonged pregnancy, or severe pre-eclampsia
What are 6 things that, if associated with shallow, late decelerations, are suggestive of a preterminal fetus?
- IUGR
- Absent fetal movements
- Bleeding
- Infection
- Prolonged pregnancy
- Severe pre-eclampsia