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	• Diabetes Mellitus (Pre-gestational & GDM) • Hypertension / Preeclampsia • Chronic Renal Disease • SLE / APLA Syndrome • Cyanotic Heart Disease
Fetal Conditions	• Intrauterine Growth Restriction (IUGR) • Multiple Gestation (Twins/Triplets) • Decreased Fetal Movements • Oligohydramnios / Polyhydramnios • Rh Isoimmunization
Obstetric Factors	• Post-term pregnancy (>42 weeks) • Previous unexplained stillbirth • 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 $\to$ 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): $\ge$ 2 accelerations of $\ge$ 15 bpm lasting $\ge$ 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) - Manning’s 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	$\ge$ 1 episode of 30 sec in 30 mins
2. Fetal Movement	$\ge$ 3 discrete body/limb movements
3. Fetal Tone	$\ge$ 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:
  • 8–10: Normal.
  • 6: Equivocal (Repeat in 24 hrs).
  • $\le$ 4: Abnormal (Consider delivery).

4. Modified BPP

• A rapid screening tool combining:
  1. NST (Acute marker)
  2. Amniotic Fluid Index (AFI) (Chronic marker)
• Normal if both are normal.

C. Doppler Velocimetry (Hemodynamic Monitoring)

Crucial for managing IUGR/FGR.

1. Umbilical Artery (UA): reflects placental resistance.
   • progression: High Resistance $\to$ Absent End Diastolic Flow (AEDF) $\to$ Reversed End Diastolic Flow (REDF).
2. Middle Cerebral Artery (MCA): reflects fetal adaptation.
   • Brain Sparing Effect: Hypoxia causes cerebral vasodilation $\to$ Decreased MCA resistance (Low PI).
3. 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 15–30 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:
  1. Baseline Rate: Normal 110–160 bpm.
  2. Variability: Most important indicator of oxygenation. Normal (Moderate) = 6–25 bpm.
  3. Accelerations: Presence ensures pH >7.20.
  4. 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 – 7.25: Borderline (Repeat in 30 mins).
  • pH <7.20: Acidosis $\to$ Immediate Delivery.
• Note: Lactate measurement is an alternative to pH.

5. SUMMARY ALGORITHM

1. High Risk Pregnancy $\to$ Start NST/BPP/Doppler.
2. Labor Onset $\to$ Continuous CTG (if high risk) or Intermittent Auscultation (low risk).
3. Abnormal CTG (Cat II) $\to$ Scalp Stimulation.
   • Reactive: Continue monitoring.
   • Non-reactive: Scalp pH or Consider Delivery.
4. Category III CTG or pH <7.20 $\to$ Expedite Delivery (C-Section/Instrumental).