7.2 Prematurity, Low Birth Weight & Neonatal Jaundice

7.2 Prematurity, Low Birth Weight & Neonatal Jaundice

UPSC CMS High-Yield Note: Neonatal morbidity and mortality in India are heavily driven by low birth weight (LBW), prematurity, respiratory complications, and hyperbilirubinemia. UPSC CMS frequently tests definitions, Kangaroo Mother Care (KMC) protocols, respiratory distress syndrome (RDS) diagnostics, Kramer's zones, phototherapy physics, and exchange transfusion calculations.

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1. Classification & Definitions

A. Based on Birth Weight

• Low Birth Weight (LBW): Birth weight $< 2500\text{ g}$ (up to and including $2499\text{ g}$), irrespective of gestational age.
• Very Low Birth Weight (VLBW): Birth weight $< 1500\text{ g}$.
• Extremely Low Birth Weight (ELBW): Birth weight $< 1000\text{ g}$.

B. Based on Gestational Age

• Preterm: Infant born before $37\text{ completed weeks}$ ($< 259\text{ days}$) of gestation.
  • Late Preterm: $34\text{ to } 36^{+6}\text{ weeks}$.
  • Moderate Preterm: $32\text{ to } 33^{+6}\text{ weeks}$.
  • Very Preterm: $28\text{ to } 31^{+6}\text{ weeks}$.
  • Extremely Preterm: $< 28\text{ weeks}$.
• Term Infant: Born between $37\text{ and } 41^{+6}\text{ weeks}$ ($259 - 293\text{ days}$).
• Post-term Infant: Born at or after $42\text{ completed weeks}$ ($\ge 294\text{ days}$).

C. Small for Gestational Age (SGA) vs. Intrauterine Growth Restriction (IUGR)

• SGA: Birth weight below the 10th percentile for gestational age.
• Symmetrical SGA (Intrinsic / Early Insult):
  • Occurs early in pregnancy (1st trimester). Caused by chromosomal anomalies, TORCH infections, or maternal drug exposure.
  • Head circumference, length, and weight are proportionately reduced. Ponderal Index ($\text{Weight in g} \times 100 / \text{Length in cm}^3$) is normal.
• Asymmetrical SGA (Extrinsic / Late Insult):
  • Occurs late in pregnancy (3rd trimester). Caused by uteroplacental insufficiency, maternal hypertension, or pre-eclampsia.
  • Weight is markedly reduced while length and head circumference are spared (Head-sparing effect). Ponderal Index is low ($< 10\text{th percentile}$).

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2. Management of Prematurity & Kangaroo Mother Care (KMC)

Preterm infants are exceptionally prone to hypothermia, apneas, feeding intolerance, necrotizing enterocolitis (NEC), intraventricular hemorrhage (IVH), and sepsis.

Kangaroo Mother Care (KMC)

KMC is an evidence-based, low-cost intervention for low birth weight and preterm infants.

• Two Essential Components:
  1. Continuous Skin-to-Skin Contact (SSC): Infant placed upright between mother's breasts in a frog-like position, secured with a binder.
  2. Exclusive Breastfeeding: Direct breastfeeding or expressed breast milk feeding.
• Eligibility: All hemodynamically stable neonates weighing $< 2000\text{ g}$. (Can be initiated even in unstable babies on CPAP once initial resuscitation is complete).
• Duration: Should be practiced for at least 1 hour per session (to avoid frequent handling stress) and as continuously as possible ($24\text{ hours/day}$) until infant reaches $2500\text{ g}$ or no longer tolerates it.
• Benefits:
  • Reduces neonatal mortality by up to $40%$ in LBW infants.
  • Maintains optimal thermal control via thermal synchrony (maternal skin temperature increases or decreases dynamically to maintain infant's temperature).
  • Reduces hospital-acquired sepsis, hypothermia, and apnea rates.
  • Enhances weight gain ($15-25\text{ g/kg/day}$) and rates of exclusive breastfeeding.

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3. Neonatal Respiratory Disorders

Antenatal Steroid Protocol for RDS Prevention

• Indication: Recommended for all pregnant women at risk of preterm delivery between 24 and 34 weeks of gestation.
• Regimen:
  • Betamethasone: $12\text{ mg}$ IM, 2 doses given 24 hours apart.
  • Dexamethasone: $6\text{ mg}$ IM, 4 doses given 12 hours apart.
• Effect: Accelerates Type II pneumocyte maturation, increasing surfactant synthesis and reducing RDS, IVH, and mortality.

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4. Neonatal Hyperbilirubinemia (Neonatal Jaundice)

Jaundice becomes clinically detectable in neonates when total serum bilirubin (TSB) exceeds $5\text{ mg/dL}$ (compared to $>2\text{ mg/dL}$ in adults).

A. Physiological vs. Pathological Jaundice

B. Differential Diagnosis of Unconjugated Hyperbilirubinemia

• Onset $< 24\text{ Hours}$ (Always Pathological):
  • ABO Incompatibility: Most common blood group incompatibility. Mother is Blood Group O, baby is Blood Group A or B. Direct Coombs Test (DCT) may be weakly positive or negative; spherocytes seen on blood smear.
  • Rh Isoimmunization: Mother is Rh-negative, baby is Rh-positive. Direct Coombs Test is strongly positive. Causes severe anemia, hydrops fetalis, and rapid jaundice.
  • TORCH Infections, G6PD deficiency, Pyruvate kinase deficiency.
• Onset Days 2 – 4: Physiological jaundice, extravasated blood (cephalhematoma), polycythemia, breast feeding jaundice (suboptimal intake leading to dehydration and increased enterohepatic circulation).
• Onset Day 4 – 7 & Beyond: Breast milk jaundice (inhibitors in breast milk such as $3\alpha,20\beta$-pregnanediol and free fatty acids; peak at 2-3 weeks, resolves by 3-12 weeks; breastfeeding should not be discontinued), Crigler-Najjar syndrome (Type I complete UGT1A1 absence; Type II partial), Gilbert syndrome, Sepsis, Hypothyroidism.

C. Differential Diagnosis of Conjugated Hyperbilirubinemia (Direct $> 2\text{ mg/dL}$)

• Biliary Atresia: Progressive obliteration of extrahepatic biliary tree. Triad: Persistent jaundice, clay-colored (acholic) stools, dark urine. Surgical procedure of choice: Kasai Portoenterostomy (most effective when performed before 60 days of life).
• Neonatal Hepatitis, Choledochal cyst, Galactosemia (cataract, hepatomegaly, reducing substances in urine), Alpha-1 Antitrypsin deficiency.

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5. Clinical Assessment: Kramer's Staging of Jaundice

Jaundice progresses in a cephalocaudal direction (head to toe).

• Zone 1: Head and Neck $\rightarrow$ TSB $\sim 4 - 8\text{ mg/dL}$
• Zone 2: Upper Trunk (down to umbilicus) $\rightarrow$ TSB $\sim 5 - 12\text{ mg/dL}$
• Zone 3: Lower Trunk and Thighs $\rightarrow$ TSB $\sim 8 - 16\text{ mg/dL}$
• Zone 4: Arms and Lower Legs $\rightarrow$ TSB $\sim 11 - 18\text{ mg/dL}$
• Zone 5: Palms and Soles $\rightarrow$ TSB $> 15 - 20\text{ mg/dL}$

Clinical Note: If jaundice involves the palms and soles (Zone 5), immediate transcutaneous or serum bilirubin estimation is mandatory as TSB is likely $> 15-20\text{ mg/dL}$.

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6. Therapeutics: Phototherapy, Exchange Transfusion & Kernicterus

A. Phototherapy

• Mechanism of Action: Light absorbed by unconjugated bilirubin in skin capillaries causes photochemical reactions:
  1. Structural Isomerization (Primary Mechanism): Converts $4Z,15Z$-bilirubin into Lumirubin (irreversible, water-soluble structural isomer excreted rapidly in bile and urine without conjugation).
  2. Photo-isomerization: Converts $4Z,15Z$ to $4Z,15E$-bilirubin (reversible, excreted in bile).
  3. Photo-oxidation: Converts bilirubin to small polar molecules.
• Light Specifications: Special blue light with wavelength $460 - 490\text{ nm}$. Distance from baby: $30 - 45\text{ cm}$.
• Precautions: Eyes covered with opaque patches (prevent retinal damage) and gonads covered.
• Complications: Loose green stools, dehydration, skin rash, hyperthermia, and Bronze Baby Syndrome (occurs if phototherapy is mistakenly given in conjugated hyperbilirubinemia due to accumulation of copper porphyrins).

B. Exchange Transfusion

• Goal: Rapidly remove circulating bilirubin, sensitized RBCs, and maternal antibodies.
• Volume: Double Volume Exchange ($2 \times 80\text{ mL/kg} = \mathbf{160\text{ mL/kg}}$). Replaces $\sim 85%$ of circulating red cells.
• Blood Selection Guidelines:
  • Rh Isoimmunization: O-negative blood crossmatched against mother, or Rh-negative blood of infant's ABO group.
  • ABO Incompatibility: O-group RBCs (of infant's Rh type) suspended in AB plasma.

C. Kernicterus (Acute Bilirubin Encephalopathy)

• Pathophysiology: Unbound, unconjugated lipid-soluble bilirubin crosses the blood-brain barrier and selectively deposits in the Basal Ganglia (specifically the Globus Pallidus), subthalamic nuclei, and auditory brainstem nuclei.
• Clinical Stages:
  • Early: Lethargy, hypotonia, poor sucking, loss of Moro reflex.
  • Intermediate: Hypertonia, fever, high-pitched cry, retrocollis, and Opisthotonos (arching of back).
  • Chronic Sequelae: Athetoid cerebral palsy, sensorineural hearing loss (SNHL), dental enamel hypoplasia, and upward gaze palsy.