Cardiotocography as a Test of Fetal Well Being Max Brinsmead MB BS PhD December 2014

The objective of CTG screening:

An ideal screening test:

CTG as a screening test

CTG as a Screening Test n Positive predictive value = the chance that a screen positive individual will have the disease n For CTG this is never more than 50% n i.e. at least 50% of the time it will be unnnecessarily alarming

A screening test is more likely to be a true positive if

It is positive in a high risk group

So always consider the clinical context

And be prepared to back up with a diagnostic test

Which, for the diagnosis of fetal hypoxia, is Scalp Blood pH or lactate

Problems with Screening: n FALSE POSITIVES – And the resources required to deal with them n UNREALISTIC EXPECATATIONS – i.e. misunderstanding about the sensitivity of the test

Meta analysis of RCTs of Intrapartum CTG monitoring n 12 Trials n In 10 centres in the US, Australia, Europe and Africa n 58,855 women and 59,324 babies n Both high and low risk pregnancies n Compared routine EFM with intermittent auscultation

Meta analysis Results n A significant decrease in: – rate of 1 minute Apgar scores less than 4 (RR = 0.82 and CI ) – Neonatal seizures (RR=0.50 and CI )

Meta analysis Results n A significant increase in: The rate of intervention by Caesarean section and operative delivery (RR=1.23 and CI ) The rate of intervention by Caesarean section and operative delivery (RR=1.23 and CI )

Meta analysis Results n No effect on: – rate of 1 min Apgar scores <7 – rate of admissions to NICU – Perinatal death rate – 5 min Apgar scores – rate of Cerebral palsy

But let us not throw out the baby with The CTG’s dirty bathwater!

Because, as a screening test for hypoxia, IT IS CURRENTLY THE BEST TEST WE HAVE

Who should have Intrapartum CTG? n Patients who have increased risk for fetal hypoxia or acidosis –Identified by antenatal factors –Intrinsic fetal problems –Develop intrapartum problems

Antenatal Risks

Intrapartum indications for CTG? n Suspected chorioamnionitis or temp >38 0 C n BP >160 systolic or 110 diastolic n Oxytocin in use n Significant meconium n Fresh vaginal bleeding n Non reassuring intermittent auscultation –But remove after 20 min if normal

Intrapartum indications for CTG? n Consider continuous CTG if 2 or more of the following occur –BP >150 systolic or 100 diastolic –Delay in the 1 st or 2 nd stage –Light meconium staining

An Examination of CTG Abnormalities What is Important

CTG Features n Baseline heart rate n Decelerations - early, late and variable n Short term variability n Accelerations

Reassuring CTG n Baseline 110 – 160 bpm n >5 bpm variability n No decelerations n Accelerations present (The absence of accelerations in an otherwise normal CTG is of uncertain significance)

Non Reassuring CTG n Baseline or bpm n Variability <5 bpm for <40 but <90 min n Variable decelerations <30 min n Single prolonged deceleration up to 3 min n Decelerations in <50% contractions

Abnormal CTG n Baseline 180 bpm n Variability 90 min n Decelerations with >50% of contractions n Variable decelerations for >30 min n Late decelerations for >30 min n Prolonged deceleration >3min or recurs n Sinusoidal for >10 min

Decelerations

Atypical Variable Deceleration n Slow return to baseline n Secondary rise in baseline n Biphasic n Loss of variability during deceleration n Continution baseline at a lower level NB The 2014 NICE guidelines have dispensed with “atypical” and “typical”

RCOG Recommendations Settings on CTG machines should be standardised, so that: Paper speed is set to 1 cm/min Paper speed is set to 1 cm/min Sensitivity displays are set to 20 bpm/cm Sensitivity displays are set to 20 bpm/cm FHR range displays of 50–210 bpm are used. FHR range displays of 50–210 bpm are used.

Categorisation of CTGs Normal =A CTG where all four features fall into the reassuring category Normal =A CTG where all four features fall into the reassuring category Suspicious =a CTG with one non reassuring feature Suspicious =a CTG with one non reassuring feature Pathological =a CTG with two or more nonreassuring features or one or more abnormal features Pathological =a CTG with two or more nonreassuring features or one or more abnormal features

RCOG and NICE

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