Disorders associated with prematurity (IRDS, NEC, Sudden Infant Death)

1. Prematurity

Defined as gestational age <37 weeks or weight <2500 g; the 2nd most common cause of neonatal mortality. Growth restriction may persist (cerebral dysfunction, learning/sensory impairment).

Causes:

• Fetal — chromosomal disorders, congenital anomalies, TORCH infections → symmetric growth restriction.
• Placental — placenta previa, abruption, infarction (uteroplacental supply failure).
• Maternal (most common) — preeclampsia, narcotics/alcohol/smoking, malnutrition/hyperglycemia.

2. Infant respiratory distress syndrome (IRDS)

• Mostly <28 weeks; associated with male sex, maternal diabetes, C-section, second twin.
• Core defect: surfactant deficiency (immature type II pneumocytes) → ↑ surface tension → alveolar collapse:
  • No surfactant → atelectasis → hypoventilation → hypoxemia + CO₂ retention → acidosis → pulmonary vasoconstriction → endothelial/epithelial damage → plasma leak → hyaline membrane (fibrin + necrotic cells) → worsening oxygenation.
• Hormonal control: corticosteroids ↑ surfactant; insulin (diabetic mother) suppresses it; labor ↑ surfactant (so C-section is a risk).
• Morphology: heavy, purple, airless lungs; eosinophilic hyaline membranes lining bronchioles/ducts/alveoli.
• Complications: retinopathy of prematurity, bronchopulmonary dysplasia (chronic O₂/ventilation injury), PDA, intraventricular hemorrhage, NEC.
• Prevention/Tx: antenatal steroids, exogenous surfactant; ↓ L/S ratio (lecithin:sphingomyelin) predicts immaturity.

3. Necrotizing enterocolitis (NEC)

• Most common serious intestinal disease of premature infants; intestinal ischemia + mucosal injury + bacterial colonization after formula feeding.
• Morphology: terminal ileum, cecum, right colon — distended, friable, congested/gangrenous; coagulative necrosis, ulceration, submucosal gas bubbles.
• Clinical: abdominal distension, bloody stools, circulatory collapse; pneumatosis intestinalis on imaging; may need resection; high mortality (perforation, sepsis).

4. Sudden infant death syndrome (SIDS)

• Unexplained death <1 year (after full autopsy, scene exam, history); usually during sleep; leading cause of death from 1 month–1 year.
• Pathogenesis: suspected arcuate nucleus hypoplasia (brainstem arousal/cardiorespiratory control) → inability to respond to noxious stimuli (hypoxia, hyperthermia).
• Risk factors: prone sleeping, soft bedding, overheating, maternal smoking, prematurity.
• Prevention: supine sleep, avoid soft bedding/overheating.
• Morphology: arcuate nucleus hypoplasia, thymic petechiae, congested lungs, pulmonary edema.

💡 High-yield: IRDS = surfactant deficiency → hyaline membrane; risks male/diabetic mother/C-section; ↓ L/S ratio; antenatal steroids + surfactant. NEC = ischemia + feeding → pneumatosis intestinalis, bloody stools. SIDS = unexplained sleep death; supine sleep prevention; arcuate nucleus.