The neonatal period is the transitional time from intrauterine to independent existence. Defined as approximately the first 4 weeks after delivery, the neonatal period is possibly the most tenuous in a human’s lifetime. Of the nearly 4 million babies who are born alive annually in the United States, approximately 1% die within the first 24 hours, 1% die within the first week, and 1% die within the first year. Behrman and Kliegman (1983) note that an infant experiences a greater risk of death during the first 7 days of life than at any other time during the next 65 years. The largest number of deaths occurring during the first year of life is attributed to sudden infant death syndrome (SIDS).

The average newborn enters the world weighing between 2,500 and 4,300 gm (5 lb 8 oz) and (9 lb 8 oz), with the overall average being about 3,200 to 3,400 gm (7 lb to 7 lb 8 oz). About 90% of newborns are approximately 46 to 56 cm (18 to 22 in) in length, with the average being about 51 cm (20 in) (O’Rahilly & Muller, 1996). The baby’s size is associated with a variety of factors including parental size, race, gender, maternal nutrition, and overall maternal health. Male newborns tend to be slightly longer and heavier than their female counterparts, and the first child in the birth order generally weighs less than any of the siblings who follow (Puckett & Black, 2004). The skin of newborns is often pale and thin. The skin also may be covered with lanugo—a light, fuzzy body hair—or vernix caseosa, an oily fluid that protects the baby from infection. Both of these substances disappear shortly after birth.

The skeletal system of the neonate is not totally developed, and consequently many of the bones are soft and pliable. For example, the fontanelles are the gaps between the bones in the skull that permit the skull bones to overlap during the birth process and allow for additional brain growth. The posterior fontanelle gradually closes up through the third month of life, whereas the anterior fontanelle is closed by 18 months of age.

The respiratory system of the newborn must adapt to a gaseous environment. Although the newborn consumes about twice the amount of oxygen as an adult does (Klaus & Fanaroff, 2001), respiration tends to be rapid, shallow, irregular, and unsynchronized, with the abdomen doing more work than the chest. The neonate may make peculiar wheezing and coughing sounds because the entire respiratory system is underdeveloped and inexperienced with the demands of the extrauterine environment. The digestive and circulatory systems also must make the transition to independent functioning. The visual system is incomplete because of underdevelopment of the retina and optic nerve; however, the newborn’s eyes can follow a moving light as well as a moving target. In general, neonates can see best at a distance of about 19 cm (71/2 in). There also seems to be a preference for visually following human faces more than any other type of object (Johnson, Dziurawiee, Ellis, & Morton, 1991) and they seem to prefer faces judged by adults to be more attractive, regardless of age, gender, or race (Slater et al., 1998). Interestingly, these features may not be as true for newborns with emergent neurodevelopmental disorders (e.g., autism).

The neonate also maintains physiological reactivity to sound intensity, as indicated by increased heart rate and motor activity, as well as an orienting reflex in which the baby turns in the direction of the sound stimulus. The other senses of olfaction, taste, and tactile sensitivity also are intact (Puckett & Black, 2004). For example, the neonate is capable of distinguishing among sweet, sour, and bitter tastes, as well as distinguishing the odor of its mother’s breast milk (Winberg & Porter, 1998). Motor skills of the neonate are mainly characterized by primitive reflexes and random gross motor activity. Reflexes are automatic inborn behaviors of which the newborn has many. Further discussion of reflexes and motor development is provided in chapters 3 and 4. Many neonates who experience medical difficulties are served in neonatal intensive care units.