gestational age

The gestational age of a newborn is the length of his or her gestation up to delivery. Now of course, gestation time is what it is; we just have no way of being very certain how long most babies actually spent in the womb. We are interested in this concept only because it helps in predicting what problems a newborn might be prone to develop. For example, 40 week gestation term babies almost never develop respiratory distress syndrome, 24 week gestation prematures essentially all do. Also, gestational age assessment helps us in understanding what went on in utero. When a 38 week gestation baby is growth retarded, for example, it implies a poor pregnancy, with possible placental problems or significant maternal health problems, maternal smoking, and so forth.

Gestational age is determined by several means. In decreasing order of accuracy, they are

  • calculation from a known date of conception
  • calculation from a standardized test such as the Dubowitz neurological exam or the Ballard scale of physical and neuromuscular maturity
  • estimation by experience - having done sufficient formal gestational age exams, most busy doctors and nurses can tell by glancing at the physical features what the gestational age is, and rarely resort to the formal test sheet
This determination is of course of most importance when the newborn is born early. We call babies premature who are born earlier than 36 weeks gestation; those 36-37 weeks are preterm; term is 38-42 weeks (40 being normal term gestation). Beyond 42 weeks gestation is postterm gestation, may herald problems with the baby related to the fact that the placenta tends to become less and less functional as gestation goes too far past the due date.

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