Assessment of fetal Well-being - Fetal Surveillance
1. INTRODUCTION
- Definition: A spectrum of prenatal and intrapartum tests designed to monitor fetal health, primarily to detect fetal hypoxia and acidosis.
- Goal: To prevent intrauterine fetal death (IUFD) and long-term neurological injury (cerebral palsy) through timely intervention.
2. CLINICAL INDICATIONS FOR SURVEILLANCE
Fetal surveillance is indicated in pregnancies where the risk of fetal demise exceeds the risk of neonatal death from prematurity.
| Category | Specific Indications |
|---|---|
| Maternal Conditions | β’ Diabetes Mellitus (Pre-gestational & GDM) β’ Hypertension / Preeclampsia β’ Chronic Renal Disease β’ SLE / APLA Syndrome β’ Cyanotic Heart Disease |
| Fetal Conditions | β’ Intrauterine Growth Restriction (IUGR) β’ Multiple Gestation (Twins/Triplets) β’ Decreased Fetal Movements β’ Oligohydramnios / Polyhydramnios β’ Rh Isoimmunization |
| Obstetric Factors | β’ Post-term pregnancy (>42 weeks) β’ Previous unexplained stillbirth β’ Antepartum Hemorrhage (APH) |
3. ANTEPARTUM FETAL MONITORING
Goal: Detect chronic hypoxia.
A. Clinical Methods
Daily Fetal Movement Count (DFMC) / "Kick Charts"
- Principle: Fetal movement is a marker of CNS integrity. Hypoxia reduces movement to conserve energy.
- Cardiff "Count-to-Ten" Formula: Mother counts movements starting at 9 AM.
- Normal: 10 movements perceived within 12 hours.
- Alarm Signal: <10 movements in 12 hours
Requires NST.
B. Bio-Physical Methods
1. Non-Stress Test (NST)
- Principle: An intact fetal CNS couples fetal movement with heart rate accelerations.
- Procedure: Fetal Heart Rate (FHR) monitored for 20 minutes using an external transducer.
- Interpretation:
- Reactive (Normal): $\geq$2 accelerations of $\geq$15 bpm lasting $\geq$15 seconds within 20 mins (>32 weeks). (10x10 for <32 weeks).
- Non-Reactive: No accelerations in 40 mins (after accounting for fetal sleep cycle).
- Implication: Reactive NST = Low probability of death in next 1 week.
2. Contraction Stress Test (CST) / Oxytocin Challenge Test
- Principle: Uterine contractions reduce uteroplacental blood flow. A compromised fetus develops Late Decelerations due to transient hypoxia.
- Procedure: 3 contractions (40-60 sec duration) in 10 mins stimulated via Nipple Stimulation or Oxytocin.
- Results:
- Negative (Good): No late decelerations.
- Positive (Bad): Late decelerations with >50% of contractions.
- Note: Rarely performed now; largely replaced by BPP and Doppler.
3. Biophysical Profile (BPP) - Manningβs Score
- Combines Real-time Ultrasound (acute + chronic markers) with NST.
- Score: Each parameter is 2 (Normal) or 0 (Abnormal). Max score 10/10.
| Parameter | Criteria (Score 2) |
|---|---|
| 1. Fetal Breathing | $\geq$1 episode of 30 sec in 30 mins |
| 2. Fetal Movement | $\geq$3 discrete body/limb movements |
| 3. Fetal Tone | $\geq$1 episode of extension with return to flexion |
| 4. Amniotic Fluid | Single vertical pocket >2 cm (Chronic hypoxia marker) |
| 5. NST | Reactive (Acute hypoxia marker) |
- Interpretation:
- 8β10: Normal.
- 6: Equivocal (Repeat in 24 hrs).
- $\leq$4: Abnormal (Consider delivery).
4. Modified BPP
- A rapid screening tool combining:
- NST (Acute marker)
- Amniotic Fluid Index (AFI) (Chronic marker)
- Normal if both are normal.
C. Doppler Velocimetry (Hemodynamic Monitoring)
Crucial for managing IUGR/FGR.
- Umbilical Artery (UA): reflects placental resistance.
- progression: High Resistance
Absent End Diastolic Flow (AEDF) Reversed End Diastolic Flow (REDF).
- progression: High Resistance
- Middle Cerebral Artery (MCA): reflects fetal adaptation.
- Brain Sparing Effect: Hypoxia causes cerebral vasodilation
Decreased MCA resistance (Low PI).
- Brain Sparing Effect: Hypoxia causes cerebral vasodilation
- Ductus Venosus (DV): reflects cardiac status.
- Abnormal 'a' wave (reversed) indicates impending heart failure/acidemia.
4. INTRAPARTUM FETAL MONITORING
Goal: Detect acute hypoxia/acidosis during labor.
A. Intermittent Auscultation (IA)
- Method: Handheld Doppler or Pinard stethoscope.
- Protocol: Every 15β30 mins in active phase; every 5 mins in second stage.
- Indication: Low-risk pregnancies.
B. Electronic Fetal Monitoring (EFM) / Cardiotocography (CTG)
- Method: Continuous tracing of FHR and Uterine Contractions.
- Key Parameters:
- Baseline Rate: Normal 110β160 bpm.
- Variability: Most important indicator of oxygenation. Normal (Moderate) = 6β25 bpm.
- Accelerations: Presence ensures pH >7.20.
- Decelerations:
- Early: Head compression (Benign).
- Late: Uteroplacental insufficiency (Hypoxia).
- Variable: Cord compression.
NICHD Classification of CTG Traces (2008 Guidelines)
| Category | Description | Management |
|---|---|---|
| Category I (Normal) | Normal baseline, Mod variability, No late/variable decels. | Routine care. |
| Category II (Indeterminate) | Tachycardia, Minimal variability, or Variable decels. | Closely monitor, intrauterine resuscitation. |
| Category III (Abnormal) | Sinusoidal pattern OR Absent variability + (Recurrent late/variable decels or Bradycardia). | Urgent Delivery. |
C. Adjunctive Tests (If CTG is Non-Reassuring)
1. Fetal Scalp Stimulation
- Gentle scratching of fetal scalp during PV exam.
- Response: Acceleration of FHR implies pH >7.20 (No acidosis).
2. Fetal Scalp Blood Sampling (FSBS)
- Gold Standard for confirming acidosis.
- Blood taken from fetal scalp via amnioscope.
- Interpretation:
- pH >7.25: Normal.
- pH 7.20 β 7.25: Borderline (Repeat in 30 mins).
- pH <7.20: Acidosis
Immediate Delivery.
- Note: Lactate measurement is an alternative to pH.
5. SUMMARY ALGORITHM
- High Risk Pregnancy
Start NST/BPP/Doppler. - Labor Onset
Continuous CTG (if high risk) or Intermittent Auscultation (low risk). - Abnormal CTG (Cat II)
Scalp Stimulation. - Reactive: Continue monitoring.
- Non-reactive: Scalp pH or Consider Delivery.
- Category III CTG or pH <7.20
Expedite Delivery (C-Section/Instrumental).