Strictly speaking, gestational age of the fetus or infant is a measurement of time in utero (inside of the uterus). Gestational age can be determined prior to birth or at birth.
Prior to birth, intrauterine fetal growth can be determined using ultrasonography by taking serial determinations of the biparietal diameter of the head and the head-to- abdomen circumference ratios.
Following birth, assessing an infant's weight, length, head circumference, condition of skin, hair, reflexes, muscle tone, posture, and vital signs can provide a 'relative' or 'developmental' gestational age. The 'developmental' gestational age may not match the calendar gestational age.
For example, an infant born with a gestational age of 36 weeks may actually have a developmental gestational age of 38 weeks, and therefore behave more like a term infant than a premature infant.
Determination of gestational age is an important factor in planning appropriate care for the fetus or infant. It provides important information regarding expected or potential problems and directly impacts the medical treatment plan for the baby.
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