Normal embryonic and fetal growth proceeds at a predictable rate throughout pregnancy. The predictability of normal intrauterine growth across similar populations at comparable altitudes has permitted the development of standardized reference curves that can be used to compare certain physical characteristics of the newborn according to estimated gestational age. These curves are then used to determine whether the newborn is small for gestational age (SGA), appropriate for gestational age (AGA), or large for gestational age.

Reduced ambient oxygen at high altitude slows gestational growth, so standards are different from those at sea level. In 1966, Lubchenco et al published intrauterine growth curves of white infants, predominantly from the middle and upper socioeconomic classes, who were born in Denver at 5000 feet above sea level. Data included birth weight, head circumference, and crown-heel length of newborns from 26 to 42 weeks’ gestational age, as estimated by the day of onset...

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