What are the recommended fetal monitoring modalities for a pregnant individual with a history of pregnancy complications, such as preeclampsia or placental abruption, at different gestational ages?

Fetal Monitoring in High-Risk Pregnancies with Prior Complications

For pregnant individuals with a history of preeclampsia or placental abruption, comprehensive ultrasound-based fetal surveillance should be initiated at diagnosis of any recurrent hypertensive disorder or at 26-32 weeks for those with prior complications, incorporating umbilical artery Doppler, fetal biometry, and amniotic fluid assessment at intervals determined by gestational age and severity of findings. 1

Initial Assessment at Diagnosis of Preeclampsia

When preeclampsia is diagnosed at any gestational age, three core ultrasound assessments must be performed immediately:

• Fetal biometry (biparietal diameter, head circumference, abdominal circumference, femur length to estimate fetal weight) 1
• Amniotic fluid volume assessment (single deepest pocket ≥2 cm is normal) 1, 2
• Umbilical artery Doppler waveform analysis to assess placental resistance 1

For early-onset preeclampsia (diagnosed <32 weeks), a detailed anatomic ultrasound should be performed since up to 20% of cases are associated with fetal or chromosomal abnormalities 1. Consider offering chromosomal microarray analysis for unexplained isolated fetal growth restriction diagnosed before 32 weeks 1.

Surveillance Intervals Based on Gestational Age and Findings

Normal Initial Assessment (No Growth Restriction)

From 24-26 weeks onward, serial monitoring should include:

• Fetal growth assessment every 2 weeks (not more frequently, as shorter intervals don't improve detection) 1
• Umbilical artery Doppler every 2 weeks if flow patterns remain normal 1
• Amniotic fluid volume assessment every 2 weeks 1

When Fetal Growth Restriction is Detected (EFW <10th percentile)

The surveillance intensity escalates based on Doppler findings:

• Weekly umbilical artery Doppler when decreased end-diastolic velocity is present (flow ratios >95th percentile) or severe FGR (EFW <3rd percentile) 1
• 2-3 times per week Doppler assessment when absent end-diastolic velocity (AEDV) is detected, as deterioration to reversed flow can occur rapidly 1
• Daily or twice-daily cardiotocography (NST) when reversed end-diastolic velocity (REDV) is present, with hospitalization and consideration for delivery 1

Late-Onset Preeclampsia (≥32 weeks)

• Continue biweekly growth scans and Doppler studies until delivery 1
• Add weekly cardiotocography after viability for FGR without AEDV/REDV 1
• Increase frequency to twice-weekly NST when AEDV/REDV or other comorbidities are present 1

Delivery Timing Based on Doppler Findings

The umbilical artery Doppler results directly determine delivery timing to balance fetal maturity against placental insufficiency:

• 37 weeks: FGR with decreased diastolic flow but without AEDV/REDV, or severe FGR with EFW <3rd percentile 1
• 33-34 weeks: FGR with absent end-diastolic velocity 1
• 30-32 weeks: FGR with reversed end-diastolic velocity 1
• 38-39 weeks: FGR with EFW between 3rd-10th percentile and normal umbilical artery Doppler 1

History of Placental Abruption Without Current Preeclampsia

For patients with prior abruption but no current hypertensive disorder:

• Initiate antepartum fetal surveillance at 32-34 weeks gestation, as this represents a high-risk condition 1, 2
• Use weekly or twice-weekly NST as standard practice, though optimal frequency lacks rigorous evidence 1, 2
• Perform modified biophysical profile (NST plus amniotic fluid assessment) as the primary surveillance method 1, 2
• Consider serial growth scans every 3-4 weeks starting at 28-32 weeks to monitor for growth restriction 1

Critical Limitations and Caveats

No antenatal testing can predict acute events such as recurrent placental abruption or cord accidents, regardless of test frequency or modality used 1, 2. A normal test result is highly reassuring with false negatives (stillbirth within 1 week of normal test) being uncommon, but surveillance cannot eliminate all risk 1, 2.

Avoid these common pitfalls:

• Do not use middle cerebral artery, ductus venosus, or uterine artery Doppler for routine clinical management decisions in early- or late-onset FGR, as evidence doesn't support their use over umbilical artery Doppler 1
• Do not perform growth scans more frequently than every 2 weeks, as this doesn't improve detection and increases false-positive diagnoses 1
• Do not use serum uric acid or level of proteinuria as indications for delivery 1

Maternal Monitoring Alongside Fetal Surveillance

Women with preeclampsia require parallel maternal assessment:

• Blood pressure monitoring with treatment target <160/110 mmHg to reduce stroke risk 1
• Twice-weekly laboratory testing (hemoglobin, platelets, liver transaminases, creatinine, uric acid) and more frequently with clinical status changes 1
• Clinical assessment for clonus and neurological symptoms 1
• Magnesium sulfate for seizure prophylaxis when severe hypertension or neurological symptoms are present 1
• Magnesium sulfate for fetal neuroprotection before 32 weeks if delivery is anticipated 1

Antenatal Corticosteroids

Administer betamethasone or dexamethasone between 24+0 and 34+0 weeks when preterm delivery is anticipated within 7 days 1. May be given up to 38+0 weeks for elective cesarean delivery, but multiple courses are not recommended 1.