Gestational age assessment can be divided into two categories: prenatal assessment and postnatal assessment. Prenatal assessment of gestational age most commonly includes careful menstrual history, physical milestones during pregnancy (e.g., uterine size, detection of fetal heart rate and movements), and prenatal tests for maturity (e.g., ultrasound, amniotic fluid studies). Nägele's rule uses the first day of the LMP to calculate the day of labor by adding 7 days to the LMP and counting back 3 months.12 This method may be inaccurate if the mother is not a good historian or has a history of irregular menses, which interferes with identification of a normal cycle.
Postnatal assessment of gestational age is done by examination of external physical and neuromuscular characteristics alone or in combination. Assessment of gestational age should be a part of every initial newborn examination.
Accurate assessment of gestational age facilitates risk assessment and identification of abnormalities and allows for earlier interventions. Dubowitz or Ballard developed the most common methods used in nurseries today. The Dubowitz method is comprehensive and includes 21 criteria using external physical (11) and neuromuscular (10) signs.16 The estimate of gestational age is best done within 12 hours of birth and is accurate within 1 week. The method is less accurate for infants born at less than 30 weeks' gestational age. The Ballard method is an abbreviated Dubowitz method that includes 12 criteria, using 6 external physical and 6 neuromuscular signs (Fig. 2-5). The New Ballard Score (NBS) was updated and modified to include newborns at gestational ages of 20 to 44 weeks and is the most commonly used method. If performed within 12 hours post-birth by an experienced examiner, it is accurate to within 1 week.11
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