Obstetric Ultrasound: Eclampsia Risk Assessment

Obstetric ultrasound with Doppler is central to stratifying risk in pre-eclampsia and impending eclampsia, a leading cause of maternal and perinatal mortality in low-resource settings. It evaluates fetal growth, amniotic fluid, and the uteroplacental and fetoplacental circulations to identify placental insufficiency and fetal compromise. Findings guide the timing of delivery and the balance between fetal maturity and maternal safety.

Indications

Known or suspected pre-eclampsia with hypertension and proteinuria
Severe features: severe hypertension, headache, visual disturbance, epigastric or right upper quadrant pain
Suspected fetal growth restriction or reduced symphysis-fundal height
Reduced fetal movements or oligohydramnios
Surveillance in early-onset pre-eclampsia to time delivery
Chronic hypertension, prior pre-eclampsia or other high-risk pregnancy requiring growth and Doppler assessment

Contraindications & Cautions

No contraindications; obstetric ultrasound is safe and non-ionising
Do not delay definitive management (magnesium sulphate, antihypertensives, delivery) of eclampsia or severe pre-eclampsia to obtain imaging
Adhere to ALARA thermal/mechanical index limits, particularly with pulsed Doppler on the fetus
Maternal habitus, oligohydramnios and fetal position may limit biometry and Doppler adequacy

Patient Preparation

No fasting required; a moderately full bladder aids early second-trimester and cervical assessment
Left lateral tilt or semi-recumbent positioning to avoid aortocaval compression and maternal hypotension
Explain the examination and its purpose; obtain verbal consent
Ensure blood pressure control and seizure prophylaxis are in hand before a prolonged study
Confirm gestational age from early dating scan or reliable menstrual data for percentile interpretation

Technique & Parameters

Curvilinear transabdominal transducer (3-5 MHz); fetal biometry: BPD, HC, AC and FL for estimated fetal weight
Amniotic fluid assessment by single deepest pocket and amniotic fluid index (AFI)
Umbilical artery pulsed Doppler in a free loop of cord: record PI/RI and end-diastolic flow (absent or reversed = severe)
Middle cerebral artery Doppler for cerebroplacental ratio and brain-sparing (redistribution)
Uterine artery Doppler lateral to the cervix at the crossing with the external iliac: pulsatility index and early diastolic notching
Ductus venosus Doppler in severely growth-restricted fetuses (absent/reversed a-wave signals decompensation); use biophysical profile as adjunct

Systematic Review

Confirm viability, number, presentation and gestational age
Fetal biometry and estimated fetal weight against growth charts (percentile)
Amniotic fluid volume (AFI and deepest pocket)
Placental location, maturity and any abruption or retroplacental haematoma
Umbilical artery, MCA and cerebroplacental ratio
Uterine artery Doppler for resistance and notching
Ductus venosus and biophysical profile in high-grade restriction

Key Findings & Significance

Oligohydramnios (AFI <5 cm or deepest pocket <2 cm): placental insufficiency
Fetal growth restriction with AC or EFW <10th percentile, worse if <3rd percentile
Raised umbilical artery PI/RI, then absent, then reversed end-diastolic flow - progressive severity
Reduced MCA PI and low cerebroplacental ratio: fetal blood-flow redistribution (brain sparing)
Bilateral uterine artery notching with high PI: impaired trophoblastic invasion and high pre-eclampsia risk
Abnormal ductus venosus a-wave: cardiovascular decompensation prompting delivery consideration

Differential Considerations

Symmetrical small fetus: constitutionally small versus early-onset placental FGR versus wrong dates
Oligohydramnios: placental insufficiency, ruptured membranes, renal anomaly, post-dates
Abnormal uterine artery Doppler: pre-eclampsia, placental disease, chronic hypertension
Retroplacental collection: abruption versus fibroid or myometrial contraction
Elevated umbilical resistance: placental insufficiency, cord abnormality, fetal anaemia
Maternal RUQ pain with ascites/subcapsular fluid: HELLP syndrome and hepatic complications

Pearls & Pitfalls

Umbilical artery reversed end-diastolic flow is an ominous sign requiring urgent obstetric decision-making
Interpret Doppler in trend, not a single value; document angle and vessel sampled
Uterine artery notching is more meaningful when persistent beyond 24 weeks
Imaging supports but never replaces clinical and biochemical severity assessment
Beware maternal supine hypotension distorting Doppler waveforms; scan in left tilt
A normal scan does not exclude rapidly progressive maternal disease - delivery may still be indicated on maternal grounds

Structured Report

State gestational age basis, fetal number, presentation and viability
Report biometry, estimated fetal weight and percentile
Document amniotic fluid, placental site and any abruption
Provide umbilical artery, MCA, cerebroplacental ratio and uterine artery Doppler indices with EDF status
Grade severity and note ductus venosus/biophysical profile where performed
Impression: integrate fetal wellbeing with maternal severity and recommend surveillance interval or delivery planning

References

ISUOG Practice Guidelines: Diagnosis and management of small-for-gestational-age fetus and fetal growth restriction
NICE Guideline NG133: Hypertension in pregnancy: diagnosis and management
ACOG Practice Bulletin: Gestational Hypertension and Preeclampsia
WHO Recommendations for Prevention and Treatment of Pre-eclampsia and Eclampsia

Educational clinical decision support only. Protocols vary by institution and equipment; always confirm with a qualified radiologist and local guidelines before clinical use.

Obstetric Ultrasound: Eclampsia Risk Assessment

📋 Indications

⛔ Contraindications & Cautions

🧑‍⚕️ Patient Preparation

⚙️ Technique & Parameters

🔎 Systematic Review

🩻 Key Findings & Significance

🧠 Differential Considerations

💡 Pearls & Pitfalls

📝 Structured Report

📚 References