Abnormal Cardiotocography

Abnormal cardiotocography is a fetal heart rate tracing that falls outside the normal range, with baseline 110 to 160 beats per minute, variability 5 to 25 beats per minute, accelerations present and no repeated decelerations.

It results from fetal hypoxia, acidosis, infection, drugs or fetal sleep. It matters because pathological tracings need action to prevent fetal injury.

Suspicious: one non reassuring feature. Pathological: two non reassuring features or one abnormal feature.

Abnormal antenatal tracings occur in growth restriction, oligohydramnios and maternal illness.

A tracing must be read with the clinical picture.

The woman may have reduced fetal movements, labour, fever, hypertension or bleeding, or have no symptoms. The abnormal tracing is found on monitoring.

Reduced variability for more than 40 minutes antenatally.

Late or prolonged decelerations in labour.

The approach is systematic tracing review with clinical correlation and tests of fetal wellbeing.

• Define baseline rate, variability, accelerations and decelerations; abnormal features: baseline below 100 or above 180 beats per minute, variability below 5 beats per minute for more than 90 minutes in labour, sinusoidal pattern for 30 minutes, late decelerations for more than 30 minutes, prolonged deceleration beyond 3 minutes.
• Antenatal: short term variation below 3.5 ms (before 32 weeks) or below 4.5 ms (after 32 weeks) on computerised tracing; no accelerations and reduced variability for more than 40 minutes.
• Ultrasound for deepest pocket, growth, umbilical artery and middle cerebral artery Doppler; biophysical profile score 6 or below is abnormal.
• Maternal temperature, blood pressure, glucose, infection tests; fetal scalp lactate in labour.

The principle is to correct reversible causes, confirm fetal condition and expedite delivery for persistently pathological tracings.

• Supportive: change maternal position to left or right lateral; stop oxytocin; two cannulae; treat hypotension; oxygen 10 L/minute by mask for a short period while preparing for delivery; empty the bladder; continuous monitoring.
• Pharmacological: Ringer's lactate 500 to 1000 mL IV over 15 to 30 minutes; terbutaline 0.25 mg subcutaneous once for tachysystole; ephedrine 5 to 10 mg IV for hypotension after epidural; paracetamol 1 g oral 6-hourly (maximum 4 g in 24 hours) for fever; ampicillin 2 g IV 6-hourly plus gentamicin 5 mg/kg IV once daily for chorioamnionitis; betamethasone 12 mg IM twice, 24 hours apart, between 24 and 34 weeks and 6 days when antenatal delivery is likely; magnesium sulphate 4 g IV over 20 minutes then 1 g per hour until delivery for 24 hours at most before 32 weeks; oxytocin 10 IU IM at birth.
• Procedures: assisted vaginal delivery when fully dilated; emergency caesarean section aiming for birth within 30 minutes of the decision for pathological tracing that does not recover within 30 to 60 minutes, and within 15 minutes for bradycardia; fetal scalp sampling where available; amnioinfusion with sodium chloride 0.9 percent 500 mL intrauterine over 30 minutes then 3 mL per minute for variable decelerations with oligohydramnios.
• Special groups: antenatal tracings in growth restriction are interpreted with Doppler findings and delivery timed by gestation; women with previous caesarean section and an abnormal tracing need immediate review for uterine rupture.
• Red flags: bradycardia beyond 3 minutes, absent variability, sinusoidal pattern, repeated late decelerations, bleeding, severe abdominal pain, maternal fever.
• Follow-up: umbilical cord blood gas at birth; newborn Apgar score and neurological examination; antenatal repeat tracing within 24 hours; review of the birth debrief.