Preterm & Low Birth Weight Infant

The preterm and low birth weight (LBW) neonate is the single most fertile area in neonatology for the exam. Mastering the definitions, thermoregulation, feeding, and the four classic complications (IVH, NEC, ROP, BPD) plus Kangaroo Mother Care (KMC) will let you answer the bulk of NEET PG neonatology MCQs. The trap most candidates fall into is conflating gestational age (preterm) with birth weight (LBW) and confusing SGA with preterm — keep these axes separate.

Definitions & classification

Two independent classification systems are used, and an infant can belong to categories in both simultaneously.

By gestational age (maturity)

Term	Gestational age
Post-term	≥ 42 weeks
Term	37 to < 42 weeks
Late preterm	34 to < 37 weeks
Moderate preterm	32 to < 34 weeks
Very preterm	28 to < 32 weeks
Extremely preterm	< 28 weeks

By birth weight (independent of gestation)

Term	Birth weight
Low birth weight (LBW)	< 2500 g
Very low birth weight (VLBW)	< 1500 g
Extremely low birth weight (ELBW)	< 1000 g
Incredibly/Micro LBW	< 750 g

High-yield: LBW is defined by weight alone (< 2500 g) regardless of gestation. A term IUGR baby weighing 2200 g is LBW but not preterm. A 35-week baby weighing 2600 g is preterm but not LBW.

By intrauterine growth (weight-for-gestational age)

Plotted on an intrauterine growth chart (e.g., Lubchenco / Fenton):

• AGA (appropriate-for-gestational age): birth weight between 10th–90th centile.
• SGA (small-for-gestational age): < 10th centile.
• LGA (large-for-gestational age): > 90th centile.

High-yield: IUGR ≠ SGA. IUGR is a process (failure to achieve growth potential in utero, a clinical/USG diagnosis); SGA is a statistical cut-off at birth (< 10th centile). A constitutionally small but healthy baby is SGA but not IUGR; an IUGR baby caught early may still be > 10th centile.

SGA / IUGR — symmetric vs asymmetric

The single most asked discriminator in this topic.

Feature	Symmetric IUGR	Asymmetric IUGR
Onset	Early (1st–2nd trimester)	Late (3rd trimester)
Insult type	Intrinsic — affects cell number (hyperplasia phase)	Extrinsic — affects cell size (hypertrophy phase)
Causes	TORCH, chromosomal anomalies, teratogens, alcohol	Utero-placental insufficiency, PIH, maternal malnutrition
Head circumference	Reduced (proportionate)	Relatively spared (brain-sparing)
Ponderal index	Normal	Low
Brain : liver ratio	Normal	Increased (brain spared, liver shrinks)
Prognosis	Worse (catch-up unlikely)	Better (catch-up growth likely)

High-yield: Ponderal index = [weight (g) × 100] / [length (cm)]³. Low PI = asymmetric (malnourished, late insult). Normal PI = symmetric.

High-yield: Asymmetric IUGR shows head-sparing ("brain-sparing effect") because of redistribution of cardiac output to brain, heart, adrenals at the expense of the abdominal viscera — detected on Doppler as increased middle cerebral artery diastolic flow and reversed umbilical artery end-diastolic flow.

Etiology & risk factors for prematurity

• Maternal: infections (UTI, bacterial vaginosis, chorioamnionitis), PIH/pre-eclampsia, anaemia, malnutrition, smoking, low socioeconomic status, extremes of maternal age, prior preterm birth.
• Uterine/placental: cervical incompetence, uterine anomalies, multiple gestation, placenta praevia, abruption, polyhydramnios.
• Fetal: congenital anomalies, fetal distress, hydrops.
• Iatrogenic: medically indicated early delivery for maternal/fetal compromise.

Why preterm/LBW babies get into trouble — pathophysiology

The problems flow directly from immaturity of every organ system:

1. Thermoregulation: large surface area-to-weight ratio, thin skin, little subcutaneous fat, scant brown fat → rapid heat loss; cannot shiver.
2. Respiration: surfactant deficiency (type II pneumocytes mature ~34–35 wk) → RDS / hyaline membrane disease; weak chest wall; immature respiratory centre → apnoea of prematurity.
3. CNS: fragile germinal matrix vessels → intraventricular haemorrhage; immature drive → apnoea.
4. GI: poor suck-swallow coordination (matures ~34 wk), gut immaturity/ischaemia → necrotising enterocolitis; feed intolerance.
5. Immune: low transplacental IgG (transferred mostly in 3rd trimester), immature neutrophil function → sepsis.
6. Eye: incomplete retinal vascularisation + hyperoxia → retinopathy of prematurity.
7. Metabolic: poor glycogen/fat stores → hypoglycaemia, hypocalcaemia; immature liver → hyperbilirubinaemia.
8. Renal: immature tubules → fluid/electrolyte instability.
9. Haematological: anaemia of prematurity (low erythropoietin, short RBC life, iatrogenic blood loss).

Clinical features of the preterm infant

• Pink, thin, shiny skin with visible veins; abundant lanugo; minimal sole creases (only anterior third).
• Soft, flat, poorly recoiling pinna; absent breast nodule.
• Females: prominent clitoris and labia minora (labia majora do not yet cover).
• Males: undescended testes, poorly rugated scrotum.
• Hypotonia, "frog-leg" posture, weak/absent primitive reflexes.

High-yield: Gestational age is estimated at birth using the New Ballard Score (extends to extremely preterm, 20–44 weeks; assesses 6 neuromuscular + 6 physical criteria).

Assessment & investigations

• Gestational age: maternal LMP + early USG (best in 1st trimester); postnatal New Ballard Score.
• Anthropometry: weight, length, head circumference plotted on growth charts (Fenton chart for preterm).
• Screening panel for the sick/VLBW neonate: blood glucose, calcium, haematocrit, bilirubin, sepsis screen (CBC, CRP, blood culture), blood gas.
• Imaging: cranial USG for IVH screening (routine in VLBW), chest X-ray for RDS ("ground-glass + air bronchogram"), abdominal X-ray for NEC.

Management — NICU principles

The mnemonic for routine preterm care priorities is "WARM SWEET PINK SAFE" (Warmth, Sugar, Sepsis-free, Pink/oxygenation, Safe transport) — but the practical pillars are below.

1. Thermoregulation

Maintain neutral thermal environment (axillary temp 36.5–37.5 °C).

High-yield: Mechanisms of neonatal heat loss = Radiation, Convection, Conduction, Evaporation. Evaporation dominates immediately after birth — hence dry the baby and remove wet linen first. Pre-warm surfaces to prevent conduction loss; use radiant warmers/incubators; for ELBW, occlusive polythene wrap and humidified incubators.

High-yield: Cold stress in a neonate → peripheral vasoconstriction, increased O₂ consumption, metabolic acidosis, hypoglycaemia, hypoxia, and worsening of RDS. Neonates produce heat by non-shivering thermogenesis via brown adipose tissue (uncoupling protein/thermogenin), not shivering.

2. Kangaroo Mother Care (KMC)

The most exam-relevant intervention.

• Definition: early, prolonged, continuous skin-to-skin contact between mother (or any caregiver) and the LBW infant, with exclusive/near-exclusive breastfeeding and early discharge.
• Eligibility (WHO): haemodynamically stable LBW baby — classically weight ≤ 2000 g; can be initiated even in babies on minimal support once stable.
• Three components: (1) skin-to-skin Kangaroo position, (2) Kangaroo nutrition (breastfeeding), (3) Kangaroo discharge/follow-up.
• Position: baby placed prone, upright, between mother's breasts, head turned to one side, hips flexed (frog position), covered.

High-yield: Proven benefits of KMC: improved thermoregulation, reduced hypothermia, sepsis/infection, hypoglycaemia, and mortality; better breastfeeding, weight gain, mother-infant bonding, and earlier discharge. 2021 WHO/iKMC trial showed mortality benefit even when started immediately in stable LBW babies. Minimum effective duration historically quoted as at least 1 hour continuous per session.

3. Feeding strategy

• Breast milk is the feed of choice — preferably mother's own milk; donor human milk if unavailable.
• ≥ 34 weeks / coordinated suck: direct breastfeeding.
• 32–34 weeks: spoon/paladai/cup feeding (suck present, coordination weak).
• < 32 weeks (or unable to suck): orogastric/nasogastric (gavage) tube feeding with expressed breast milk.
• < 28–30 weeks / sick / unstable: total parenteral nutrition (IV fluids), with minimal enteral ("trophic") feeds introduced early to promote gut maturation.
• Human Milk Fortifier (HMF): added to breast milk for VLBW (< 1500 g) once on full enteral feeds, to meet high protein/calcium/phosphate/calorie needs.

Feeding decision flow: Assess maturity & stability → < 28 wk / sick → IV fluids + trophic feeds → 30–32 wk → orogastric tube EBM → 32–34 wk → spoon/paladai → ≥ 34 wk → breastfeeding → fortify if VLBW → monitor for feed intolerance/NEC.

High-yield: Supplement preterm/LBW infants with vitamin D, iron (from ~2 months/8 weeks), and a multivitamin; iron prophylaxis is essential because of poor iron stores and anaemia of prematurity.

4. Other supportive care

• Surfactant (intratracheal, e.g., poractant alfa) for RDS; antenatal corticosteroids (betamethasone/dexamethasone) to the mother 24–34 wk dramatically reduce RDS, IVH, NEC, and mortality.
• CPAP/oxygen with targeted saturation 90–95% to avoid hyperoxia (ROP risk).
• Caffeine citrate — drug of choice for apnoea of prematurity (also reduces BPD).
• Strict asepsis, judicious antibiotics, fluid/glucose/calcium monitoring.

The four classic complications

Intraventricular haemorrhage (IVH)

• Bleeding from the fragile subependymal germinal matrix (most active < 32–34 wk; involutes by term).
• Risk highest in first 72 hours; precipitated by BP fluctuations, hypoxia, hypercarbia.
• Papile grading (cranial USG): I – germinal matrix only; II – into ventricle, no dilatation; III – into ventricle with dilatation; IV – intraparenchymal extension (worst).
• Sequelae: post-haemorrhagic hydrocephalus, periventricular leukomalacia, cerebral palsy.

Necrotising enterocolitis (NEC)

• Ischaemic-inflammatory bowel necrosis; risk factors: prematurity, formula feeding, hypoxia, rapid feed advancement.
• Presents 2nd–3rd week: abdominal distension, bilious aspirates, blood in stool, lethargy.
• Investigation of choice: abdominal X-ray — hallmark pneumatosis intestinalis (intramural gas); portal venous gas; pneumoperitoneum if perforated.
• Staging: Bell's criteria (I suspected, II definite, III advanced/perforation).
• Management: NPO, orogastric decompression, IV fluids, broad-spectrum antibiotics; surgery for perforation/necrosis.

High-yield: Pneumatosis intestinalis on plain abdominal X-ray is pathognomonic of NEC. Breast milk is protective; formula increases risk.

Retinopathy of prematurity (ROP)

• Abnormal retinal neovascularisation from incomplete vascularisation + relative hyperoxia.
• Screening: indirect ophthalmoscopy — Indian guideline: birth weight < 2000 g or gestation < 34 weeks (or risk factors), first screen by 2–3 weeks (≤ 4 weeks) of life.
• Classified by zone, stage (1–5), and "plus" disease; "plus disease" (dilated, tortuous posterior vessels) indicates aggressive disease.
• Treatment: laser photocoagulation of avascular retina (current first-line); anti-VEGF (intravitreal bevacizumab/ranibizumab) in selected cases.

High-yield: Uncontrolled supplemental oxygen is the key modifiable risk factor for ROP — maintain SpO₂ 90–95%, avoid wide swings. ROP is a leading cause of preventable childhood blindness.

Bronchopulmonary dysplasia (BPD) / chronic lung disease

• Definition: oxygen dependence at 36 weeks postmenstrual age (or > 28 days of O₂ in older definition).
• Multifactorial: baro/volutrauma, oxygen toxicity, inflammation, immaturity (arrest of alveolar development = "new BPD").
• Management: minimise ventilator injury, gentle ventilation, caffeine, nutrition, judicious diuretics; vitamin A may help.

Other complications (quick map)

• RDS / hyaline membrane disease: surfactant deficiency; CXR ground-glass + air bronchogram; treat with surfactant + CPAP.
• PDA: left-to-right shunt; treat with fluid restriction + indomethacin/ibuprofen/paracetamol (COX inhibitors).
• Hypoglycaemia / hypocalcaemia: poor stores; monitor and correct.
• Hyperbilirubinaemia: immature liver conjugation; phototherapy at lower thresholds.
• Anaemia of prematurity, sepsis, hypothermia, fluid/electrolyte disturbances.

High-yield: Mnemonic for preterm complications — "RIBBON": RDS, IVH, BPD, Bilirubin (jaundice) + NEC, Ophthalmic (ROP), Nutrition/hypoglycaemia & sepsis.

Key differentials & distinctions

• Preterm AGA vs term SGA: both may be LBW. Preterm has immaturity features (lanugo, fused eyelids if very preterm, hypotonia); term SGA looks mature but wasted (loose skin, scaphoid abdomen, alert facies). SGA babies are prone to polycythaemia, hypoglycaemia, hypothermia, meconium aspiration, whereas preterm babies dominate with RDS, IVH, NEC, ROP, apnoea.
• RDS vs transient tachypnoea of newborn (TTN): RDS in preterm, progressive, ground-glass CXR; TTN in late-preterm/term (often C-section), self-limiting, fluid in fissures/streaky CXR.
• NEC vs spontaneous intestinal perforation (SIP): SIP is earlier, focal, often in ELBW on indomethacin, no pneumatosis.

Recently asked / exam angle

• Definitions are tested directly: match VLBW = < 1500 g, ELBW = < 1000 g; "LBW is defined by weight, not gestation."
• KMC eligibility weight (≤ 2000 g) and its benefits (reduced mortality/hypothermia/sepsis).
• Ponderal index formula and which IUGR type has a low PI (asymmetric).
• Symmetric vs asymmetric IUGR causes (TORCH/chromosomal = symmetric; placental insufficiency/PIH = asymmetric).
• Pneumatosis intestinalis = NEC (investigation of choice = X-ray abdomen); Bell's staging.
• Papile grading of IVH; germinal matrix as the source.
• ROP screening criteria (BW < 2000 g or GA < 34 wk; screen by 2–4 weeks) and laser as treatment; SpO₂ target 90–95%.
• Caffeine = drug of choice for apnoea of prematurity.
• Antenatal corticosteroids reduce RDS, IVH, NEC, mortality (24–34 wk).
• New Ballard Score for gestational age assessment; brown fat/non-shivering thermogenesis for heat production.
• Heat loss mechanisms; evaporative loss greatest at birth → dry immediately.

Rapid revision

1. LBW < 2500 g, VLBW < 1500 g, ELBW < 1000 g — defined by weight alone, independent of gestation.
2. Preterm = < 37 weeks; extremely preterm = < 28 weeks.
3. SGA = < 10th centile (statistical); IUGR = failure to reach growth potential (process) — not synonymous.
4. Symmetric IUGR = early, intrinsic (TORCH, chromosomal), normal ponderal index; asymmetric = late, placental insufficiency, low ponderal index, head-sparing.
5. Ponderal index = weight × 100 / length³.
6. Neonates produce heat by non-shivering thermogenesis via brown fat (thermogenin); cannot shiver. Dry baby first to cut evaporative loss.
7. KMC: skin-to-skin, breastfeeding, early discharge; eligible at ≤ 2000 g, stable; reduces hypothermia, sepsis, mortality.
8. Feeds: ≥ 34 wk breastfeed; 32–34 wk paladai/spoon; < 32 wk orogastric tube EBM; sick/<28 wk IV + trophic feeds; fortify VLBW; give iron + vitamin D.
9. IVH arises from the germinal matrix, graded by Papile (I–IV), highest risk first 72 hrs.
10. NEC: abdominal X-ray shows pneumatosis intestinalis; staged by Bell's criteria; breast milk protective, formula a risk.
11. ROP: screen if BW < 2000 g or GA < 34 wk by 2–4 weeks; treat with laser; keep SpO₂ 90–95% to avoid hyperoxia.
12. BPD = O₂ dependence at 36 weeks PMA; caffeine is drug of choice for apnoea (and reduces BPD); antenatal steroids cut RDS/IVH/NEC/mortality.