Fetal Bradycardia

Fetal bradycardia is a fetal heart rate below 110 beats per minute for more than 10 minutes, and a prolonged deceleration is a fall below 80 beats per minute lasting more than 3 minutes. Causes include cord prolapse or compression, placental abruption, uterine rupture, maternal hypotension, uterine hyperstimulation, maternal hypothermia and drugs, and congenital heart block. It matters because it is an emergency that can lead to fetal death or brain injury within minutes.

• Heart rate below 80 beats per minute for 3 minutes or more needs immediate action.
• Risk factors: induced or augmented labour, previous caesarean scar, abnormal lie, epidural anaesthesia, maternal anti-Ro or anti-La antibodies.
• Sustained rates of 50 to 80 beats per minute in the antenatal period suggest heart block.

The heart rate falls below 110 beats per minute on auscultation or cardiotocography, and the woman may have severe pain, bleeding, hypotension, a prolapsed cord, tetanic contractions or a drug history.

• Constant pain with a firm uterus suggests abruption.
• Sudden pain, loss of contractions and recession of the presenting part suggest uterine rupture.
• Differential diagnosis: cord prolapse, cord compression, placental abruption, uterine rupture, maternal supine hypotension, uterine hyperstimulation, maternal hypothermia, maternal beta blocker use, fetal heart block, long QT syndrome, maternal heart rate misread.
• Complications: fetal hypoxia, hypoxic ischaemic encephalopathy, cerebral palsy, stillbirth, neonatal death, maternal haemorrhage.

The approach is to confirm the rate, check the maternal pulse and find the cause in minutes.

• Heart rate by Pinard, hand-held Doppler or cardiotocography, with the maternal pulse checked simultaneously to avoid misreading.
• Immediate vaginal examination for cord prolapse, full dilatation and presenting part; speculum for bleeding.
• Maternal blood pressure, pulse, temperature, uterine tone and tenderness; ultrasound for fetal heart rate, rhythm and placenta.
• Antenatal bradycardia: maternal anti-Ro and anti-La antibodies, fetal echocardiography, maternal ECG for long QT.

The principle is immediate intrauterine resuscitation and delivery within 15 minutes if the rate does not recover by 9 minutes.

• Supportive: call senior obstetric, anaesthetic and paediatric staff; left lateral or knee chest position; stop oxytocin; two cannulae; oxygen 10 L/minute by mask; empty the bladder; check blood pressure every 2 minutes; prepare theatre.
• Pharmacological: Ringer's lactate 500 to 1000 mL IV over 15 minutes; ephedrine 5 to 10 mg IV or phenylephrine 50 to 100 micrograms IV for hypotension; terbutaline 0.25 mg subcutaneous once for uterine hyperstimulation or cord prolapse; tranexamic acid 1 g IV over 10 minutes and blood transfusion for abruption; for fetal heart block with myocarditis or hydrops, dexamethasone 4 mg oral once daily until delivery; hydroxychloroquine 200 mg oral 12-hourly from early pregnancy in the next pregnancy for women with lupus or anti-Ro antibodies and an affected baby; oxytocin 10 IU IM at birth.
• Procedures: cord prolapse: push the presenting part up manually, fill the bladder with 500 to 750 mL sodium chloride 0.9 percent through a catheter, knee chest position and emergency caesarean section; assisted vaginal delivery if fully dilated with the head low; emergency caesarean section aiming for birth within 15 minutes of the decision for persisting bradycardia, abruption or uterine rupture; laparotomy for uterine rupture; newborn resuscitation; pacing of newborn with complete heart block.
• Special groups: women with previous caesarean section and bradycardia need immediate review for uterine rupture; fetal complete heart block needs delivery at term by caesarean section in a unit with neonatal pacing.
• Red flags: rate below 80 beats per minute for 3 minutes, cord prolapse, bleeding with pain, loss of contractions, maternal collapse, absent fetal heart.
• Follow-up: umbilical cord blood gas at birth; newborn Apgar score, resuscitation record and neurological examination over 72 hours; maternal review at 6 weeks and counselling about the next birth.