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Gestational Age

By Eric Gibson, MD, Nemours/Alfred I. duPont Nemours Hospital for Children, Thomas Jefferson University ; Ursula Nawab, MD, Thomas Jefferson University/Nemours

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Gestational age and growth parameters (see Growth Parameters in Neonates ) help identify the risk of neonatal pathology. Gestational age (menstrual age, postmenstrual age) is the time elapsed since the beginning of the woman's last menstrual period; it is usually counted in weeks. Because it is not based on the moment of fertilization, which is difficult to specify (except when in vitro fertilization is done), gestational age is not the actual age of the fetus. Gestational age is the primary determinant of organ maturity.

The best way to assess gestational age is with antenatal ultrasonography and menstrual history. Clinicians also estimate gestational age during the newborn physical examination (see The First Few Hours) using the new Ballard score (see Figure: Assessment of gestational age—new Ballard score.). The Ballard score is based on the neonate's physical and neuromuscular maturity and can be used up to 4 days after birth (in practice, the Ballard score is usually used in the first 24 h) . The neuromuscular components are more consistent over time because the physical components mature quickly after birth. However, the neuromuscular components can be affected by illness and drugs (eg, Mg sulfate given during labor).

Assessment of gestational age—new Ballard score.

Scores from neuromuscular and physical domains are added to obtain total score. (Adapted from Ballard JL, Khoury JC, Wedig K, et al: New Ballard score, expanded to include extremely premature infants. The Journal of Pediatrics 119(3):417–423, 1991; used with permission of the CV Mosby Company.)

Based on gestational age, each neonate is classified as

  • Premature: < 34 wk gestation (see Premature Infant )

  • Late pre-term: 34 to < 37 wk (see Late Preterm Infant )

  • Early term: 37 0/7 wk through 38 6/7 wk

  • Full term: 39 0/7 wk through 40 6/7 wk

  • Late term: 41 0/7 wk through 41 6/7 wk

  • Postterm: 42 0/7 wk and beyond

  • Postmature: > 42 wk (see Postmature Infant )

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* This is the Professional Version. *