Chapter 5 – Growth: Charts, Percentiles, and Curves

Length, weight, and head circumference are the three key parameters used to evaluate a child’s health at birth and growth during the first three years of life. To ensure the growth process is proceeding regularly, the pediatrician records these measurements over time on auxological growth charts, which help monitor growth curve trends.

Each chart’s central curve represents the average value of the reference population, while the other curves (called percentiles) show the distance from the average—either lower or higher. For example, a child in the 50th percentile for weight is right on the average, while one in the 70th percentile weighs more than peers, and one in the 30th percentile weighs less.

Percentile interpretation allows the pediatrician not only to assess a child’s position compared to the average, but more importantly, to evaluate growth consistency and regularity over time. What truly matters is the trajectory: healthy growth is reflected by the child’s adherence to their own growth curve, without sudden deviations or prolonged slowdowns.

Growth Spurts: Phases of Physiological Acceleration

During early childhood, growth is not constant or linear but alternates with temporary accelerations, known as growth spurts. These are normal phases in which the child experiences rapid gains in weight, length, and sometimes head circumference, along with behavioral and nutritional changes.

These spurts are governed by a complex hormonal system involving: Growth hormone (GH), Thyroid hormones, Sex hormones, Insulin-like growth factor (IGF-1). These hormones affect bone, muscle, and nervous tissue, enhancing cell division, bone mineralization, and nervous system development.

In addition to physical development, growth spurts play a key role in neurocognitive and motor maturation. The infant brain, which rapidly develops during the early years, uses these periods to gain new skills, refine coordination, and sharpen sensory abilities.

Typical signs of a growth spurt include:

• Increased appetite and more frequent feeding;
• Changes in sleep patterns;
• Greater restlessness or irritability;
• Rapid acquisition of new motor or cognitive abilities.

These are temporary and physiological, ma possono influenzare l’andamento delle curve di crescita, motivo per cui è fondamentale che il pediatra le riconosca e le distingua da condizioni patologiche.

Though each child has a unique rhythm, the following are typical phases of increased growth frequency:

• 1st week of life
• 3–4 weeks
• 3 months
• 6 months
• 9 months
• 12 months
• 18 months
• 2 years

During these times, it is normal to observe rapid weight or height acceleration, followed by periods of stabilization.

Growth Curves and Reference Standards

To properly assess a child’s growth, the pediatrician must use auxological curves appropriate to the child’s age, sex, and population group. In Italy, the official reference curves are those from the World Health Organization (WHO), published in 2006 and applicable from birth to five years of age.

WHO curves represent ideal growth standards, based on how children should grow under optimal conditions. The reference sample includes 8,500 children of various ethnicities, all sharing a common lifestyle: Regular pediatric checkups, Balanced nutrition with exclusive breastfeeding for the first 4–6 months, and Continued breastfeeding combined with appropriate complementary feeding up to 12 months.

Unlike the older 1977 NCHS (National Center for Health Statistics) curves, which were based on formula-fed U.S. children, WHO curves are globally applicable and not tied to a specific geographic area.

A multinational study (including Italy) found that healthy newborns born at the same gestational age show similar measurements, regardless of ethnicity, parental height, or geographic region. Based on this, anthropometric charts by sex and gestational age were developed—especially useful for preterm infants or those with intrauterine growth restriction.

Growth Monitoring Over Time

Preterm or low-birth-weight infants may initially fall into lower percentiles but often catch up by age two. It’s the pediatrician’s role to closely monitor auxological parameters – weight, height, and head circumference – especially in the first two years. Afterwards, focus shifts to weight and height

Besides absolute numbers, it’s crucial to observe longitudinal trends: a consistent curve without abrupt changes is the best sign of healthy, physiological growth.

In the first few months, weight gain is especially rapid. According to WHO standards, a newborn may gain 400g to over 800g per month in the first three months. From three months on, growth slows slightly. On average, birth weight doubles by 4–6 months and triples by the end of the first year.