Assessment of Gestational Age (GA) in Newborn

Accurate assessment of gestational age is critical for anticipating morbidity, guiding management (e.g., respiratory support, feeding), and distinguishing prematurity from growth restriction (SGA).

1. Prenatal Assessment (Gold Standard)

• First Trimester Ultrasound (CRL): Most accurate method (±3–5 days) if performed <14 weeks.
• Last Menstrual Period (LMP): Naegele’s rule; often unreliable due to irregular cycles or recall bias.

2. Postnatal Assessment: The New Ballard Score (NBS)

The standard tool for postnatal GA assessment, valid for neonates from 20 to 44 weeks. It assesses 6 neuromuscular and 6 physical criteria.

• Timing: Ideally performed within 12–24 hours of life. For infants <26 weeks, perform within 12 hours.
• Scoring: Range from -10 (20 weeks) to 50 (44 weeks). Accuracy is ±2 weeks.

A. Neuromuscular Maturity (Reflects development of passive tone; progression is hypotonia → hypertonia)

1. Posture: Observation of resting position (extension vs. flexion).
2. Square Window: Flexion of hand at wrist (90° → 0°).
3. Arm Recoil: Passive extension and release of elbow.
4. Popliteal Angle: Flexion of knee on thigh (180° → <90°).
5. Scarf Sign: Elbow position relative to midline when pulling arm across chest.
6. Heel to Ear: Resistance when drawing foot toward ear.

B. Physical Maturity (Reflects anatomical changes)

1. Skin: Sticky/transparent (preterm) → Leathery/cracked/wrinkled (post-term).
2. Lanugo: None → Abundant → Mostly bald.
3. Plantar Surface: Smooth → Red marks → Creases over entire sole.
4. Breast: Imperceptible → Full areola/bud (5–10 mm).
5. Eye/Ear: Fused lids/flat pinna → Open eyes/stiff cartilage with instant recoil.
6. Genitals (Male): Flat scrotum/undescended testes → Deep rugae/pendulous testes.
7. Genitals (Female): Prominent clitoris/flat labia → Major cover minora and clitoris.

3. Other Methods

• Examination of Anterior Vascular Capsule of Lens: Direct ophthalmoscopy. Accurate for 27–34 weeks.
  • Grade 1: Vessels cover entire anterior lens surface (27–28 wks).
  • Grade 4: Vessels usually invisible/at periphery (33–34 wks).
• Parkin’s Score: Uses 4 physical signs (skin color, texture, breast, ear); faster but less precise.