Non-Stress Test (NST) vs. Biophysical Profile (BPP)

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Both the Non-Stress Test (NST) and the Biophysical Profile (BPP) are fetal surveillance tests used in pregnancy to assess fetal well-being, especially in high-risk pregnancies. However, they differ in their components, method of assessment, and diagnostic value.

1. Non-Stress Test (NST)

Definition

The NST is a non-invasive test that monitors the fetal heart rate (FHR) in response to fetal movements. It helps assess oxygenation and autonomic nervous system function without inducing contractions.

Components

  • Fetal heart rate (FHR) pattern: Measured via an external Doppler transducer.
  • Fetal movement: Mother reports fetal kicks during monitoring.
  • Reactivity: A normal fetus should show acceleration of heart rate with movement.

Interpretation

Reactive NST (Normal):

At least 2 accelerations of FHR (≥15 bpm above baseline lasting ≥15 sec) within 20 minutes.

Indicates adequate oxygenation and neurological function.

Non-Reactive NST (Abnormal):

No significant FHR accelerations in 40 minutes.

May indicate fetal distress, requiring further evaluation with a BPP or Contraction Stress Test (CST).

Advantages

Simple, quick (20–40 minutes).

Non-invasive, painless.

Can be done in an outpatient setting.

Uses

  • Routine fetal surveillance in high-risk pregnancies (e.g., diabetes, hypertension, intrauterine growth restriction (IUGR), post-term pregnancy).
  • Assessing fetal distress when decreased fetal movements are reported.

2. Biophysical Profile (BPP)

Definition

The BPP is a more comprehensive test that combines an NST with an ultrasound examination to evaluate multiple aspects of fetal health.

Components (Scoring System: 0 or 2 points for each parameter, Max = 10 points)

1. NST (FHR Reactivity) – Assesses fetal oxygenation and nervous system function.

2. Fetal Breathing Movements – At least one episode of breathing for ≥30 sec in 30 minutes.

3. Gross Fetal Movements – At least 3 discrete body/limb movements in 30 minutes.

4. Fetal Muscle Tone – At least one episode of active extension and flexion of limbs.

5. Amniotic Fluid Volume (AFV) – At least one pocket of fluid measuring ≥2 cm in vertical depth.

Interpretation

8–10 points → Normal (low risk of fetal distress).

6 points → Equivocal (requires further monitoring or repeat testing).

4 points or less → Abnormal, possible fetal distress, delivery may be considered.

Advantages

  • More comprehensive than NST alone.
  • Can detect chronic fetal hypoxia earlier than NST.
  • Helps in decision-making regarding urgent delivery if distress is suspected.

Uses

  1. Used when an NST is non-reactive.
  2. Monitoring high-risk pregnancies (e.g., preeclampsia, IUGR, oligohydramnios, post-term pregnancy).
  3. Evaluating prolonged decreased fetal movements.

Clinical Application

  • Start with NST → If reactive, no further testing is needed.
  • If NST is non-reactive, proceed to BPP for a more detailed assessment.
  • If BPP score is ≤4, immediate intervention (e.g., delivery) may be required.

Conclusion

Both tests are essential tools in prenatal care, especially for high-risk pregnancies. NST is quick and useful for screening, while BPP provides a more detailed evaluation, guiding decisions about timing of delivery and fetal health management.

Location: Nigeria

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