17.9: Infancy (Birth to Age One)

Several significant physiological changes occur during infancy. The body’s trunk grows faster than the arms and legs, while the head becomes less prominent than the limbs. Organs and organ systems grow at a rapid rate. Also, during this period, countless new synapses form to link brain neurons. Two soft spots on the baby’s skull, known as fontanels, allow the skull to accommodate rapid brain growth. The posterior fontanel closes first, by the age of eight weeks. The anterior fontanel closes about a year later, at eighteen months on average. Developmental milestones include sitting up without support, learning to walk, teething, and vocalizing, among many others. These changes require adequate nutrition to ensure development at the appropriate rate.

Healthy infants grow steadily but not always at an even pace. For example, during the first year of life, height increases by 50 percent, while weight triples. Physicians and other health professionals can use growth charts to track a baby’s development process. Because infants cannot stand, the length is used instead of height to determine a child’s growth rate. Other vital developmental measurements include head circumference and weight. These must be tracked and compared against standard measurements for an infant’s age.

For infants and toddlers from birth to 24 months of age, the World Health Organization (WHO) growth charts monitor growth. These standards represent optimal growth for children at this age and track growth trends over time through percentile rankings. Growth charts may warn that a child has a medical problem or is malnourished. Insufficient weight or height gain during infancy may indicate a condition known as failure-to-thrive (FTT), characterized by poor growth. FTT can happen at any age, but it typically occurs after six months in infancy. Some causes include poverty, lack of food, inappropriate feeding foods, and excessive fruit juice intake.

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