Why is a Kleihauer (Kleihauer-Betke) test performed in cases of decreased fetal movements?

Why Perform a Kleihauer-Betke Test in Decreased Fetal Movements?

The Kleihauer-Betke test should be performed in cases of decreased fetal movements to detect fetomaternal hemorrhage (FMH), which can cause life-threatening fetal anemia that may be treatable with emergency delivery or intrauterine transfusion if identified promptly.

Primary Rationale: Detection of Fetomaternal Hemorrhage

The Kleihauer-Betke test identifies fetal red blood cells in maternal circulation, diagnosing FMH as a potentially reversible cause of fetal compromise 1. This is critical because:

• FMH can cause severe fetal anemia leading to hydrops fetalis or intrauterine death, but is treatable with intravascular transfusion or immediate delivery 1
• Decreased fetal movements are a cardinal presenting symptom of significant FMH, reported in approximately 50% of cases 2, 3, 4, 5
• Even massive FMH (>30 mL/kg) can present with normal ultrasound findings including normal Manning scores (68.4%), normal middle cerebral artery velocities (26.7%), and normal fetal heart rate patterns (22.7%) 4

Clinical Context and Urgency

Decreased fetal movements warrant increased fetal surveillance as they are associated with increased risk of stillbirth 1. The American College of Radiology guidelines specifically list maternal perception of decreased fetal movement as an indication for antepartum testing 1.

When FMH is Suspected

The Society for Maternal-Fetal Medicine recommends maternal Kleihauer-Betke testing as part of the workup for nonimmune hydrops fetalis in structurally normal fetuses 1. The test should be performed when:

• Decreased fetal movements are accompanied by non-reassuring fetal heart rate patterns (particularly sinusoidal patterns, though these are not always present) 2, 6, 5
• Non-stress testing is non-reactive in the setting of decreased movements 2, 5
• Ultrasound evaluation is being performed for decreased movements 3, 5

Diagnostic Performance and Clinical Utility

Recent evidence demonstrates the Kleihauer-Betke test's value:

• Excellent sensitivity and negative predictive value (100%) for severe neonatal anemia, though positive predictive value is lower 3
• Better than MCA-PSV Doppler for predicting any neonatal anemia, while MCA-PSV is superior for predicting moderate to severe anemia 3
• Positive in only 0.9% of cases when performed for decreased fetal movements, but identifies the critical cases requiring intervention 3
• The volume of FMH relative to fetal weight is the best predictor of need for postnatal transfusion 4

Critical Management Implications

When FMH is diagnosed via positive Kleihauer-Betke test:

• Immediate delivery should be considered if gestational age is viable and FMH volume exceeds 140 mL, particularly with non-reassuring fetal status 2
• Intravascular fetal transfusion can be lifesaving even with massive FMH, and should be performed unless advanced gestational age makes delivery safer 1
• All live-born infants with massive FMH survive with appropriate intervention, though 78.3% require transfusion 4
• Neurological outcomes are generally good when FMH is promptly recognized and treated 2, 6, 5

Recommended Diagnostic Algorithm

When a patient presents with decreased fetal movements 3, 5:

1. Perform non-stress testing as initial assessment
2. If non-reactive or concerning, order Kleihauer-Betke test along with detailed ultrasound
3. Include middle cerebral artery Doppler (MCA-PSV) to assess for fetal anemia 1, 3
4. If MCA-PSV suggests anemia or Kleihauer-Betke is positive, proceed urgently to delivery or intrauterine transfusion depending on gestational age and severity 1

Important Caveats

• Normal ultrasound and fetal heart rate do not exclude significant FMH - the Kleihauer-Betke test may be the only diagnostic clue 4
• Antenatal surveillance cannot predict acute events like FMH, which is why testing must be performed when symptoms arise 1
• The test has low positive predictive value (many positive tests will not result in severe anemia), but the consequences of missing FMH are catastrophic 3
• MCA-PSV Doppler may suffice as first approach, with Kleihauer-Betke performed to confirm FMH if fetal anemia is suspected 3