Signs of Failure to Thrive in Babies
The short answer
Failure to thrive (now often called growth faltering) refers to a baby or child who is not gaining weight as expected. It is typically defined as weight falling below the 2nd percentile, or crossing down two or more major percentile lines on the growth chart. While it sounds alarming, most cases are related to feeding difficulties, inadequate calorie intake, or transient illness, and can be successfully treated. Early identification and intervention are important for optimal outcomes.
Parents everywhere have the same worry. You are doing the right thing by looking into it.
By Age
What to expect by age
0-3 months
In the first weeks, some weight loss after birth is normal (up to 7-10% of birth weight), with most babies regaining birth weight by 10-14 days. After that, babies typically gain about 5-7 ounces per week. Common causes of poor weight gain at this age include breastfeeding difficulties (latch issues, low milk supply), inadequate feed volumes, tongue tie, or medical conditions affecting absorption. Your pediatrician monitors weight closely at well-child visits. If your baby is not back to birth weight by 2 weeks, additional feeding support is usually recommended.
3-12 months
Weight gain naturally slows after the first 3-4 months, from about 5-7 ounces per week to about 3-5 ounces per week. A baby who was gaining well and then plateaus may be experiencing a change in milk supply, difficulty transitioning to solids, a food allergy, chronic reflux, or recurrent illness. Growth chart trends matter more than any single measurement. If your baby crosses down two percentile lines, your doctor will want to investigate. Increasing calorie density of feeds and ensuring adequate feeding frequency are common first interventions.
12-36 months
Weight gain slows further in the toddler years, and normal toddlers may appear leaner as they become more active. However, a toddler who continues to fall on the growth chart, is significantly underweight, or has decreased energy warrants evaluation. Picky eating, excessive juice or milk intake (displacing solid food), undiagnosed food allergies or celiac disease, and chronic infections can contribute. Your pediatrician may order blood tests and possibly refer to a pediatric gastroenterologist or feeding specialist.
What Should You Do?
When to take action
- Your baby lost some weight in the first few days after birth but regained it by 2 weeks.
- Your baby is on a lower percentile on the growth chart but is following their own consistent curve.
- Weight gain slows somewhat between 4-6 months as your baby becomes more active.
- Your baby seems to be eating well but is not gaining weight as expected.
- Your baby has crossed down one major percentile line on the growth chart.
- Your baby is feeding frequently but still seems hungry, unsatisfied, or excessively fussy.
- You are concerned about your breast milk supply or your baby's formula intake.
- Your newborn has not regained birth weight by 2-3 weeks of age.
- Your baby has fewer than 4 wet diapers in 24 hours, appears dehydrated, or is lethargic.
- Your baby has crossed down two or more major percentile lines on the growth chart.
- Your baby is losing weight, has visible wasting (loss of fat and muscle), or seems increasingly weak or unresponsive.
Sources
Related Resources
Trust your instincts. If something feels wrong, reach out to your pediatrician.
Worrying about your baby means you care. That is a good thing.
Related Feeding Concerns
My Baby Has Chronic Diarrhea with No Infection
Chronic diarrhea in babies and toddlers without infection is relatively common and is often due to functional causes like toddler's diarrhea (functional diarrhea), dietary factors, or food sensitivities. Toddler's diarrhea is the most common cause of chronic diarrhea in children ages 1-5 and typically resolves on its own. However, persistent diarrhea should be evaluated to rule out less common causes like celiac disease, food allergies, or malabsorption conditions.
When Does My Baby Need Amino Acid Formula?
Amino acid-based formulas (also called elemental formulas) are prescribed for babies with severe cow's milk protein allergy, multiple food protein intolerances, or conditions like eosinophilic esophagitis who cannot tolerate standard or extensively hydrolyzed formulas. They are the most hypoallergenic formula available because the proteins are broken down into individual amino acids, making allergic reactions virtually impossible.
Preventing Dehydration in Babies During Hot Weather
Babies are more vulnerable to dehydration and heat-related illness because they have a higher metabolic rate and less efficient temperature regulation. For babies under 6 months, extra breast milk or formula feeds (not plain water) are the best way to maintain hydration in hot weather. Signs of dehydration include fewer than 4 wet diapers in 24 hours, dry mouth, no tears when crying, sunken fontanelle, and lethargy. Always keep babies out of direct sunlight and never leave them in a parked car.
Baby Refusing Breast
A baby refusing the breast can be stressful, but it is usually temporary and has a fixable cause. Common reasons include a stuffy nose, teething pain, an ear infection, change in milk taste, or overstimulation. This is different from weaning, which is gradual. Most breast refusal episodes resolve within a few days with patience, skin-to-skin contact, and addressing the underlying cause.
When to Introduce Allergens to Baby
Current guidelines recommend introducing common allergens (peanut, egg, cow's milk products, tree nuts, wheat, soy, fish, shellfish, sesame) starting around 4-6 months when your baby is developmentally ready for solids. The landmark LEAP study showed that early introduction of peanuts (by 4-6 months) reduced peanut allergy risk by 80% in high-risk infants. Do not delay allergens - the old advice to wait until 1-3 years has been reversed because early exposure actually prevents allergies.
I'm Worried My Baby Is Aspirating During Feeds
Aspiration means liquid or food enters the airway instead of the stomach. Occasional coughing during feeds is common and does not usually indicate aspiration. True aspiration is less common and may present as recurrent respiratory infections, a wet or gurgly voice after feeds, or chronic cough. If you are concerned, a swallow study can provide a definitive answer.