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)
- Posture: Observation of resting position (extension vs. flexion).
- Square Window: Flexion of hand at wrist (90° → 0°).
- Arm Recoil: Passive extension and release of elbow.
- Popliteal Angle: Flexion of knee on thigh (180° → <90°).
- Scarf Sign: Elbow position relative to midline when pulling arm across chest.
- Heel to Ear: Resistance when drawing foot toward ear.
B. Physical Maturity (Reflects anatomical changes)
- Skin: Sticky/transparent (preterm) → Leathery/cracked/wrinkled (post-term).
- Lanugo: None → Abundant → Mostly bald.
- Plantar Surface: Smooth → Red marks → Creases over entire sole.
- Breast: Imperceptible → Full areola/bud (5–10 mm).
- Eye/Ear: Fused lids/flat pinna → Open eyes/stiff cartilage with instant recoil.
- Genitals (Male): Flat scrotum/undescended testes → Deep rugae/pendulous testes.
- 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.