The transition from uterine to extrauterine life happens in moments. The initial breath is probably triggered by changes in pressure on the thorax during birth. Fluid is squeezed from the lungs and replaced by a rush of air. Within 1 minute, the brain stem picks up signals about the rise and fall of arterial oxygen and carbon dioxide, triggering a gasping breath and crying. The child’s lungs clear, promoting the conversion from fetal to infant heart-lung circulation. Sensory changes such as air temperature, noise, and light also contribute to the first breath.

Apgar scores are used as a rough assessment of immediate adjustment to extrauterine life. Heart rate, respirations, muscle tone, reflexes, and skin color are assessed at 1 and 5 minutes after birth, with each being given a score of 0, 1, or 2 (Figure 22-1). Total scores lower than 3 indicate severe stresses. Scores of 4 to 6 signify moderate difficulty, and scores of 7 to 10 indicate no difficulty in adapting to extrauterine life. Apgar scores are affected by prematurity and maternal medication, but are not indicative of the presence or absence of neurological or physical abnormalities. Figure 22-2 cites normal vital signs in newborns.

During the first 24 hours after birth, healthy newborns undergo predictable changes in physiological and behavioral processes. The first period of reactivity covers the initial 6 to 8 hours. For the first 30 minutes, infants are highly active. They cry, suck their fists, and pass meconium and urine. Mucus secretions, heart rate, and respirations increase. Infants then become attentive to their surroundings, with eyes open, and will nurse vigorously.