Extensive physiologic changes accompany the birth process, sometimes revealing conditions that posed no problem during intrauterine life. For that reason, a person with resuscitation skills must attend each birth. Each neonate is classified as premature, full-term, or postmature to help determine the risk of various complications.

Gestational age, the primary determinant of organ maturity, can be determined in the days immediately after birth using the Ballard score (see Fig. 1: Approach to the Care of Normal Infants and Children: Assessment of gestational age—new Ballard score.). Through plotting of weight vs gestational age (see Fig. 1: Perinatal Problems: Level of intrauterine growth based on birth weight and gestational age of liveborn, single, white infants.), each infant is classified as small, appropriate, or large for gestational age. Head circumference and length are also plotted against gestational age (see Fig. 2: Perinatal Problems: Level of intrauterine growth based on gestational age, body length (A), and head circumference (B) at birth.). These parameters are influenced by genetic factors and intrauterine conditions. They also help to predict subsequent growth and development.

Fig. 1
Level of intrauterine growth based on birth weight and gestational age of liveborn, single, white infants. Point A represents a premature infant. Point B indicates an infant of similar birth weight who is mature but small for gestational age. The growth curves represent the 10th and 90th percentiles for all of the neonates in the sampling. (Adapted from Sweet AY: Classification of the low-birth-weight infant. In Care of the High-Risk Neonate, ed. 3, edited by MH Klaus and AA Fanaroff. Philadelphia, WB Saunders Company, 1986; used with permission.)

Fig. 2
Level of intrauterine growth based on gestational age, body length (A), and head circumference (B) at birth. (Adapted from Lubchenco LC, Hansman C, Boyd E: Intrauterine growth in length and head circumference as estimated from live births at gestational ages from 26 to 42 weeks. Pediatrics 37:403, 1966; reproduced by permission of Pediatrics.)

Last full review/revision March 2007 by James W. Kendig, MD