Growth Patterns in Infants

Introduction to Growth Rates

Healthy term neonates typically gain approximately 30 grams per day during the first 3 months of life, with a growth rate that follows a predictable pattern: 0-3 months: ~30 g/day and 3-6 months: ~20 g/day 1
Breastfed infants show different growth patterns compared to formula-fed infants, with faster weight gain in the first few months but slower gain after approximately 3 months, while formula-fed infants may show more consistent weight gain patterns but might gain weight more rapidly after 3 months 2

The World Health Organization (WHO) growth charts should be used for children from birth to 2 years, and the Centers for Disease Control and Prevention (CDC) charts for children from age 2 years onward, as recommended by the Centers for Disease Control and Prevention guidelines 3
When plotting weight gain, consider weight-for-age, length-for-age, and weight-for-length, as recommended by the World Health Organization 2
Failure to thrive is defined as weight below the 10th percentile for age, weight that crosses two or more major percentile lines downward on standard growth charts, or weight-for-height below the 10th percentile, according to the American Academy of Pediatrics guidelines 4
Weight below 70% of expected weight-for-height (Z-score < -3) is an indicator of severe malnutrition, as stated by the MMWR Recommendations and Reports 5

The first-line approach for patients with inadequate oral intake is oral nutritional supplements, with regular reassessment to determine continued need, as recommended by Clinical Nutrition guidelines 6
When oral interventions fail, enteral tube feeding should be considered, with individualized route, formula, and timing, according to Clinical Nutrition guidelines 6
Parenteral nutrition should be reserved for exceptional cases when enteral feeding is not possible, such as short-term use following major GI surgery or for severely compromised patients awaiting transplantation, as stated by Clinical Nutrition guidelines 6
The recommended daily intake for severely malnourished children requiring therapeutic feeding is 150 kcal and 3g protein per kg body weight/day, divided into 4-6 meals per day, as per the MMWR Recommendations and Reports 5
Energy requirements can be calculated using Schofield's equation to determine resting energy expenditure (REE), and then adding factors for physical activity and catch-up growth, or by doubling the REE, as recommended by the American Academy of Pediatrics guidelines 7

The frequency of assessment for children with failure to thrive is as follows: infants: every clinic visit, older children and adolescents: every 3 months, and adults: every 6 months, as recommended by Clinical Nutrition guidelines 6
Premature infants should have their weight gain monitored closely, with an expected weight gain of 17-20 g/kg/day, as suggested by the American Academy of Pediatrics 3
Extremely preterm infants (born before 28 weeks gestation) have different growth patterns and higher risk of failure to thrive, and should be evaluated using adjusted age and appropriate growth charts, as recommended by the American Academy of Pediatrics guidelines 8
Children with severe malnutrition (weight-for-height Z-score < -3) and medical instability should be referred to the emergency room immediately, as per the MMWR Recommendations and Reports 5

The American Academy of Pediatrics guidelines define the following levels of care for newborns with failure to thrive:

Level of Care	Description
Level I	Well Newborn Nursery: can stabilize newborns with FTT until transfer to higher level of care
Level II	Special Care Nursery: appropriate for infants ≥32 weeks gestation and ≥1500g with moderate illness expected to resolve rapidly
Level III	NICU: required for infants <32 weeks, <1500g, or with critical illness regardless of gestational age
Level IV	Regional NICU: for cases requiring complex surgical intervention or specialized care

The American Academy of Pediatrics recommends that children with failure to thrive be treated with a focus on nutritional rehabilitation and addressing specific etiologies to improve morbidity, mortality, and quality of life outcomes, although the specific citation for this is ignored, similar recommendations are made by 3 and 9
Children with severe malnutrition should be treated with a high-energy and high-protein diet, with close monitoring of electrolytes and weight gain, as suggested by the World Health Organization, with similar guidance provided by 3 and 9
The estimated energy requirements for catch-up growth are:
The recommended weight gain target for children with failure to thrive is 17-20 grams/kg/day 7