Abnormal Umbilical Artery Doppler

Abnormal umbilical artery Doppler is a raised pulsatility index (above the 95th centile for gestation), or absent or reversed end diastolic flow, in the umbilical artery.

It reflects increased resistance in the placental villous vessels from obliteration of the small vessels. It matters because it identifies growth restricted fetuses at high risk of hypoxia, stillbirth and perinatal death.

• Normal flow falls in resistance with gestation, with forward flow in diastole throughout.

• Raised index with forward flow carries lower risk than absent or reversed flow.

• Risk factors: preeclampsia, hypertension, thrombophilia, smoking, antiphospholipid syndrome.

Women are usually asymptomatic, with small fundal height, reduced fetal movements or hypertension. The Doppler result is found at a growth scan.

• Often associated with growth restriction.
• Oligohydramnios in advanced disease.
• Differential diagnosis: technical error (probe angle, fetal movements, apnoea), constitutionally small fetus, early onset growth restriction, chromosomal abnormality, cord entanglement.
• Complications: stillbirth, fetal acidosis, preterm birth, intrapartum hypoxia, neonatal death.

The approach is a repeat Doppler with growth assessment.

• Umbilical artery Doppler in a free loop during fetal rest, repeated in 24 to 48 hours; pulsatility index above the 95th centile defines it.
• Estimated fetal weight, abdominal circumference, liquor volume, middle cerebral artery Doppler, cerebroplacental ratio, ductus venosus Doppler when flow is absent or reversed.
• Maternal tests: blood pressure, urine protein, full blood count, platelets, antiphospholipid antibodies, malaria rapid test.
• Cardiotocography at diagnosis.

The principle is surveillance by Doppler and cardiotocography and delivery by the flow pattern.

• Supportive: daily fetal movement counts; left lateral rest; stop smoking; admit for absent or reversed flow after 26 weeks.
• Pharmacological: labetalol 200 mg oral every 8 to 12 hours (maximum 2.4 g daily) or nifedipine modified release 30 to 60 mg oral once daily (maximum 120 mg) for hypertension; betamethasone 12 mg IM twice, 24 hours apart, between 24 and 34 weeks and 6 days when delivery is planned; magnesium sulphate 4 g IV over 20 minutes then 1 g per hour until delivery for 24 hours at most before 32 weeks; enoxaparin 40 mg subcutaneous daily with aspirin 150 mg oral at night for antiphospholipid syndrome; aspirin 150 mg oral at night from 12 weeks to 36 weeks in the next pregnancy.
• Procedures: delivery at 37 weeks for raised index with forward flow, at 34 weeks for absent flow, at 30 to 32 weeks for reversed flow; earlier for pathological cardiotocography or abnormal ductus venosus; induction with misoprostol 25 micrograms vaginal 6-hourly (maximum 4 doses) or Foley catheter for forward flow with continuous cardiotocography.
• Special groups: preeclampsia needs magnesium sulphate for severe features and labetalol 20 mg IV then 40 mg, 80 mg and 80 mg at 10 minute intervals (maximum 220 mg) for blood pressure 160/110 mmHg or more.
• Red flags: absent or reversed end diastolic flow, reduced fetal movements, oligohydramnios, abnormal cardiotocography, severe hypertension.
• Follow-up: Doppler weekly (twice weekly if worsening); growth every 2 weeks; cardiotocography twice weekly.