Gestational Age Assessment
Overview
Gestational age assessment determines a newborn's true maturity independent of maternal dates, which can be inaccurate. The New Ballard Score is the standard tool, combining six neuromuscular criteria (posture, square window, arm recoil, popliteal angle, scarf sign, heel to ear) and six physical criteria (skin, lanugo, plantar creases, breast tissue, ear cartilage, genitalia) for a score corresponding to 20-44 weeks. It is most accurate within 12-48 hours of birth; after 96 hours neuromuscular findings shift as the infant adapts to extrauterine tone. Once gestational age is set, the newborn is plotted on a growth curve and classified SGA, AGA, or LGA — and that classification, not the weight alone, drives nursing surveillance.
Interpretation
More creases, more cartilage, more flexion means more mature. Gestational age (weeks) and weight classification (SGA/AGA/LGA) are independent — a preterm infant can be LGA and a term infant can be SGA.
weeks
During — Monitoring
Weight classification drives risk
SGA
- Percentile
- <10th
- Glucose risk
- hypoglycemia
- Other key risk
- polycythemia, hypothermia
AGA
- Percentile
- 10th-90th
- Glucose risk
- baseline
- Other key risk
- lowest risk
LGA
- Percentile
- >90th
- Glucose risk
- hypoglycemia
- Other key risk
- birth injury
Patient Teaching
Clinical Pearl
Date the maturity, not the scale: more creases, more cartilage, more flexion mean more mature — then plot the weight, because a floppy infant with smooth soles arrived early and a term infant at 2,100 g is SGA hunting for hypoglycemia.