Gestational-age assessment of the newborn
Gestational age (GA) describes maturity at birth and guides respiratory support, feeding, thermoregulation, medication, jaundice thresholds and follow-up. The best estimate is based on reliable menstrual dates and early ultrasound; physical and neuromuscular examination is a complementary method when dates are uncertain.
Record both the best obstetric estimate and the postnatal examination estimate, including the method and uncertainty.
Definitions
| Category | Completed gestation | Clinical implications |
|---|---|---|
| Preterm | Less than 37+0 weeks | Respiratory, thermal, feeding, infection and neurodevelopmental risks |
| Very preterm | Less than 32 weeks | High need for specialised neonatal care |
| Extremely preterm | Less than 28 weeks | Very high morbidity/mortality; specialist counselling |
| Term | 37+0 to 41+6 weeks | Assess size, transition and post-term risks |
| Post-term | 42+0 weeks or more | Meconium, macrosomia, placental insufficiency and birth injury risks |
Best dating information
- Use first-trimester ultrasound when available.
- Use a certain last menstrual period if cycles are regular and recall is reliable.
- Use assisted-reproduction dates when applicable.
- Correlate fundal height and fetal growth but do not use them alone to date a newborn.
- If no reliable date exists, perform a validated examination such as New Ballard or Dubowitz and document uncertainty.
Physical maturity assessment
- Skin: transparency, colour, texture, peeling and cracking.
- Lanugo: fine hair distribution changes with maturity.
- Plantar creases: absent/sole smoothness progresses to deep creases.
- Breast tissue: areola and bud size.
- Eye/ear: eyelid opening, pinna cartilage and recoil.
- Genitalia: testicular descent/scrotal rugae or labial development.
Neuromuscular maturity assessment
- Posture and resting flexion.
- Square-window angle at the wrist.
- Arm recoil after flexion.
- Popliteal angle.
- Scarf sign.
- Heel-to-ear manoeuvre.
More flexion, stronger recoil, resistance to extension and limited heel-to-ear movement indicate greater maturity. Perform gently; pain, illness, hypoxia, neuromuscular disease, sedation and severe growth restriction can distort the estimate.
Ballard/Dubowitz approach
Validated scores assign points to physical and neuromuscular signs and convert the total to an estimated GA. New Ballard is practical at the bedside, especially when dates are unavailable, but precision is limited and accuracy is lower in extremely preterm infants or when examination is delayed. Use the score to guide care—not to overrule reliable early ultrasound.
Management implications
- Preterm babies need aggressive thermal protection, respiratory assessment, feeding support and infection vigilance.
- GA changes bilirubin treatment thresholds and risk interpretation.
- Medication doses, caffeine, antibiotics, fluids and nutrition depend on GA/postnatal age and organ function.
- Arrange hearing, eye, developmental, immunisation and growth follow-up appropriate to GA and birth weight.
- Explain uncertainty honestly to caregivers and update the estimate if better records become available.
Exam pearls
- Early ultrasound is more reliable than late physical scoring.
- Neuromuscular signs are especially useful when dates are unknown.
- Illness and sedation can make a mature infant appear immature.
- Always interpret weight relative to gestational age.
References
- SlideShare: Assessment of gestational age.
- WHO newborn and preterm-care guidance.
- New Ballard/Dubowitz clinical assessment principles.
