Failure to Thrive
Paediatrics · Growth & Development · lean revision notes
Failure to Thrive
Failure to thrive (FTT), better termed faltering growth, describes an infant or young child whose weight gain and/or growth fall significantly below expected norms for age and sex. It is a sign, not a diagnosis — the exam task is always to classify it (organic vs non-organic), evaluate sensibly, and rehabilitate nutritionally.
High-yield: FTT is fundamentally a problem of inadequate calories — whether from insufficient intake, inadequate absorption, or increased metabolic demand/loss. Memorise these three buckets; nearly every cause slots into one.
Definition & diagnostic criteria
There is no single universally accepted definition, and NEET PG loves this ambiguity. The commonly tested anthropometric criteria are:
| Criterion | Threshold for FTT |
|---|---|
| Weight for age | < 3rd (or < 5th) percentile on > 1 occasion |
| Weight | Drop across ≥ 2 major percentile lines on a standardised growth chart |
| Weight for length / BMI | < 5th percentile |
| Weight | < 80% of ideal (median) body weight for age (Gomez-type cut-off) |
| Rate of gain | Below expected velocity for age over time |
High-yield: The single most sensitive parameter affected first in FTT is WEIGHT. Sequence of derangement: weight → length/height → head circumference (last and most ominous). Early head-circumference sparing favours nutritional cause; early HC involvement suggests an intrauterine, genetic, or CNS cause.
Order of parameter involvement (flow):
Weight falls first → then linear growth (stunting) if chronic → finally head circumference (microcephaly) in severe/prolonged deprivation →
This sequence underlies the classic distinction between wasting (acute, low weight-for-height) and stunting (chronic, low height-for-age).
High-yield: A drop crossing two or more percentile lines is the most frequently quoted single-statement definition in MCQs.
Classification
1. By mechanism (the most testable framework)
| Mechanism | Examples |
|---|---|
| Inadequate caloric intake | Poor feeding technique, incorrect formula dilution, neglect, poverty, breastfeeding difficulties, cleft palate, oromotor dysfunction, anorexia of chronic disease, mechanical (large tonsils) |
| Inadequate absorption / increased losses | Coeliac disease, cystic fibrosis, cow's milk protein allergy, chronic diarrhoea, short-gut, biliary atresia, IBD, pancreatic insufficiency |
| Increased metabolic demand | Congenital heart disease, chronic lung disease (BPD), hyperthyroidism, chronic infection (TB, HIV, UTI), malignancy, chronic anaemia, inborn errors of metabolism |
| Defective utilisation | Genetic syndromes, metabolic disorders, chromosomal anomalies |
2. By aetiology — organic vs non-organic (classic exam dichotomy)
| Feature | Non-organic (psychosocial) | Organic |
|---|---|---|
| Frequency | ~80% of cases (commonest overall) | ~20% |
| Cause | Neglect, poverty, poor feeding, maternal depression, deprivation | Identifiable medical disease |
| History | Disturbed feeding, social adversity | Symptoms of underlying illness (vomiting, diarrhoea, recurrent infection) |
| Examination | Often signs of neglect, "frozen watchfulness", poor hygiene | Disease-specific signs |
| Response to feeding in hospital | Rapid catch-up weight gain when fed adequately | Limited/no gain unless disease treated |
| Investigations | Usually normal | Often abnormal |
High-yield: The commonest cause of FTT overall is non-organic (inadequate intake due to psychosocial/feeding factors), NOT a hidden organic disease. Over-investigation is a classic wrong answer.
High-yield: A child who shows brisk catch-up growth on supervised refeeding in hospital has, by definition, a non-organic cause — this is both diagnostic and therapeutic.
A mixed category exists: e.g., a chronically ill child whose carers also under-feed. Modern paediatrics increasingly avoids the rigid organic/non-organic split in favour of the intake–absorption–demand model, but the dichotomy remains heavily tested.
Aetiology & pathophysiology
Energy balance is the unifying concept: net energy = intake − (losses + expenditure). A sustained negative balance forces the body to catabolise fat then muscle, halting weight gain. If prolonged, linear growth slows (the body prioritises survival over height), and finally brain growth is compromised.
Key disease-specific pearls frequently asked:
- Coeliac disease — FTT + diarrhoea + abdominal distension beginning after introduction of wheat-containing weaning foods; anti-tissue transglutaminase (anti-tTG IgG) antibodies; biopsy shows villous atrophy. Classic in toddlers.
- Cystic fibrosis — FTT + steatorrhoea + recurrent chest infections; pancreatic exocrine insufficiency; diagnosed by sweat chloride.
- Cow's milk protein allergy — FTT + eczema + blood/mucus in stool + vomiting in infancy.
- Congenital heart disease (CHD) — large left-to-right shunts (VSD, AVSD, PDA) cause FTT via increased work of breathing, feeding fatigue, and increased metabolic demand. Weight is affected before length.
- Chronic kidney disease / renal tubular acidosis — growth failure with metabolic acidosis; RTA is a classic "FTT with normal-anion-gap acidosis + failure to acidify urine."
- Recurrent UTI in infants — an easily missed organic cause; always include urine culture.
- Hypothyroidism — causes poor linear growth (short stature) more than wasting; weight may even be relatively preserved.
- TORCH / intrauterine causes — present with symmetrical IUGR and early head-circumference involvement (distinguishes from postnatal nutritional FTT).
High-yield: In constitutional growth delay and familial short stature, the child is small but the growth velocity is normal and weight-for-height is normal — these are NOT FTT. FTT specifically implies poor weight gain / falling across percentiles.
High-yield: Differentiate FTT (weight affected first, normal velocity threatened) from short stature/growth retardation (height the primary problem). In endocrine causes (GH deficiency, hypothyroidism) the child is typically short but overweight-for-height (chubby), whereas in caloric FTT the child is thin/wasted.
Clinical features
The picture depends on chronicity and cause:
- Acute (wasting): thin child, decreased subcutaneous fat (buttocks, thighs), loose skin folds, prominent ribs, preserved height.
- Chronic (stunting): proportionate small size, low height-for-age.
- Signs of deprivation/neglect: poor hygiene, nappy rash, "frozen watchfulness", reduced eye contact, developmental delay, behavioural feeding problems, lack of stranger anxiety, infantile posture (hands held in flexion).
- Signs pointing to organic disease: dysmorphism, organomegaly, cardiac murmur, respiratory signs, abdominal distension, jaundice, recurrent infections.
- Developmental impact: delayed milestones, especially if severe and early.
A focused dietary history (24-hour recall, feed type, formula preparation, breastfeeding pattern, mealtime behaviour) and psychosocial history (carer mental health, family stress, finances, who feeds the child) are the highest-yield parts of the work-up.
Diagnosis & investigation of choice
High-yield: History and examination — especially a detailed feeding/dietary history and plotting on a growth chart — diagnose the majority of FTT. Laboratory tests rarely add value when history and exam are unremarkable. "Extensive lab panel" is the trap answer.
Stepwise diagnostic approach:
- Confirm faltering growth — plot serial weight, length/height, and head circumference on a standardised (WHO/IAP) chart; calculate weight-for-height. Use corrected age in preterm infants.
- Detailed history — diet (calorie count), feeding behaviour, GI symptoms, recurrent infections, antenatal/birth history, family heights, psychosocial assessment.
- Thorough examination — anthropometry, dysmorphism, systemic exam, signs of neglect, developmental screen.
- Observe a feed — directly watch feeding technique and child–carer interaction.
- Trial of adequate feeding (often as inpatient observation) — catch-up growth essentially confirms non-organic cause.
- Targeted investigations only if organic cause suspected or no catch-up on adequate intake.
First-line / screening investigations (only when indicated): FBC + film, urea & electrolytes, creatinine, LFTs, calcium/phosphate, blood glucose, urinalysis + urine culture, thyroid function, coeliac serology (anti-tTG), CRP/ESR, blood gas (for RTA). Stool examination if diarrhoea.
Second-line / directed: sweat chloride (CF), echocardiography (CHD), karyotype/genetic testing, HIV test, Mantoux/CXR (TB), small-bowel biopsy (coeliac), neuroimaging.
High-yield: Urine routine + culture is the classic "do-not-miss" screening test in an infant with unexplained FTT and no localising signs — occult UTI is a sneaky organic cause.
Management / treatment of choice
The cornerstone is multidisciplinary and centres on nutritional rehabilitation, while treating any identified organic cause.
Management flow:
Plot & confirm → identify mechanism (intake/absorption/demand) → optimise calories (catch-up feeding) → treat organic cause if present → address psychosocial factors / dietitian / health-visitor input → monitor catch-up growth on serial charting →
Nutritional principles
- Aim for catch-up growth, requiring calories above normal maintenance — roughly 150% (and up to 200%) of expected energy requirement for the child's expected (ideal) weight, not actual weight.
- A practical formula: Catch-up calories (kcal/kg/day) = RDA for age × ideal weight for height ÷ actual weight.
- Increase caloric density (e.g., fortify feeds, energy-dense formula, add high-calorie supplements) rather than just volume in poor feeders.
- Continue/optimise breastfeeding; correct formula over-dilution.
- Treat micronutrient deficiencies; start refeeding cautiously and watch for refeeding syndrome in severely malnourished children.
High-yield: Refeeding syndrome — rapid reintroduction of feeds in a severely malnourished child causes intracellular shift of phosphate, potassium, and magnesium with insulin surge → hypophosphataemia (hallmark), hypokalaemia, hypomagnesaemia, fluid overload, cardiac failure, arrhythmia. Prevent by starting feeds slowly and supplementing phosphate/thiamine.
Setting
- Most managed as outpatients with dietitian and health-visitor support.
- Admit if: severe malnutrition, suspected serious organic disease, safeguarding/neglect concern, refeeding-syndrome risk, or failure to respond to outpatient management (also serves as a diagnostic trial).
Severe acute malnutrition (WHO) — frequently combined with FTT MCQs
High-yield: WHO 10-step management of severe acute malnutrition: treat/prevent (1) hypoglycaemia, (2) hypothermia, (3) dehydration, (4) electrolyte imbalance, (5) infection, (6) micronutrient deficiency (vitamin A; iron only in rehabilitation phase, NOT initially), (7) cautious feeding, (8) catch-up growth, (9) sensory stimulation, (10) follow-up. ReSoMal is the recommended rehydration solution (lower sodium, higher potassium).
Complications
- Developmental and cognitive delay — the most important long-term consequence, especially if FTT is early, severe, and prolonged (brain growth affected).
- Behavioural and emotional problems; attachment difficulties.
- Reduced immunity → recurrent infections (vicious cycle).
- Short stature if chronic stunting persists.
- Micronutrient deficiencies (iron, zinc, vitamin A, vitamin D).
- Refeeding syndrome during rehabilitation.
- In neglect-related cases: ongoing safeguarding risk.
Key differentials
High-yield: Distinguishing "small but normal" children from true FTT is the single commonest MCQ theme. Master the table below.
| Condition | Weight gain / velocity | Weight-for-height | Distinguishing clue |
|---|---|---|---|
| Failure to thrive | Poor; crosses percentiles down | Low (wasted) | Falling weight curve; identifiable intake/absorption/demand problem |
| Familial short stature | Normal velocity | Normal | Short parents; bone age = chronological age; normal predicted height matches mid-parental height |
| Constitutional growth delay | Normal velocity (after early dip) | Normal | "Late bloomer"; delayed bone age; delayed puberty; family history of late maturation |
| Endocrine short stature (GHD, hypothyroidism) | Poor height velocity | Normal/high (chubby) | Short + overweight-for-height; low height velocity with preserved weight |
| IUGR / SGA | May catch up by age 2 | Variable | Antenatal onset; symmetrical (early HC involvement) vs asymmetrical |
| Genetic syndromes | Poor | Variable | Dysmorphism, developmental delay, abnormal HC |
A clean rule of thumb: in nutritional FTT the child is thin; in endocrine/genetic short stature the child is short but not wasted (often plump).
Mnemonics & named concepts
- Mechanism mnemonic — "In, Out, Up": Inadequate intake, Out (losses/malabsorption), Up (increased metabolic demand). Covers almost every cause.
- Parameter sequence — "WLH": Weight → Length → Head circumference (order of involvement; HC last and worst).
- Causes of inadequate intake — "FED POorly": Feeding technique, Eating/oromotor problem, Dilution error, Psychosocial neglect, Oral aversion.
- Gomez classification (weight-for-age vs reference median): Grade I 75–90%, Grade II 60–75%, Grade III < 60% — links FTT to PEM grading.
- Waterlow classification: uses wasting (weight-for-height) and stunting (height-for-age) separately — high yield for distinguishing acute vs chronic malnutrition.
Recently asked / exam angle
- "Earliest/most sensitive parameter affected in FTT?" → Weight. (And HC is affected last/most ominously.)
- "Commonest cause of FTT?" → Non-organic (inadequate caloric intake / psychosocial).
- "A child gains weight rapidly on hospital feeding — likely cause?" → Non-organic FTT (and this confirms the diagnosis).
- "Best initial investigation in unexplained infantile FTT with no localising signs?" → Urine routine + culture (occult UTI); broadly, history & dietary assessment first, not a lab panel.
- "Calories needed for catch-up growth?" → ~150% (up to 200%) of requirement, calculated for ideal/expected weight.
- Refeeding syndrome → hypophosphataemia is the hallmark electrolyte abnormality; classic linked MCQ.
- WHO SAM management → do not give iron in the initial stabilisation phase; ReSoMal for rehydration; vitamin A on admission.
- Short but chubby child with poor height velocity → think endocrine (GH deficiency/hypothyroidism), NOT nutritional FTT.
- FTT + steatorrhoea + recurrent chest infection → cystic fibrosis (sweat chloride).
- FTT + diarrhoea/distension after starting wheat → coeliac disease (anti-tTG, villous atrophy).
Rapid revision
- FTT = faltering weight gain; a sign, not a diagnosis — classify it.
- Three mechanisms: inadequate intake, inadequate absorption/increased loss, increased demand.
- Commonest cause overall is non-organic (poor intake / psychosocial), ~80%.
- Parameter order of involvement: weight → length → head circumference (HC last and most ominous).
- Diagnostic single-liner: drop across ≥ 2 major percentile lines OR weight < 3rd–5th percentile.
- History + dietary assessment + growth chart diagnose most cases; avoid the "big lab panel" trap.
- Rapid catch-up on supervised feeding = confirms non-organic cause.
- Don't-miss screening test: urine culture (occult UTI) in unexplained infantile FTT.
- Catch-up growth needs ~150% of calorie requirement for ideal weight.
- Refeeding syndrome → hallmark hypophosphataemia (+ low K⁺, Mg²⁺); refeed slowly, give thiamine.
- Short + chubby + low height velocity = endocrine cause; thin/wasted = nutritional FTT.
- Worst long-term complication = developmental/cognitive delay; WHO SAM care withholds iron initially, uses ReSoMal and vitamin A.