Physiology of the newborn

Question 1

Gestational age assessment (GAA)

Answer 1

Term newborn: 37-41 weeks
Preterm newborn < 37 wks
Post-term newborn > 41 wks
Normal birth weight: 3250 +/- 700 g
Large for gestational age: Infants born at a weight greater than 90th percentile for age
IUGR, SGA: infants born at weight < 10th percentile

Question 2

Why do we do GAA?

Answer 2

To detect abnormal fetal growth patterns. Can be determined by physical criteria, neurologic criteria, intrauterine length, weight, head circumference

Question 3

1st day assessment

Physical criteria

Answer 3

• Increased firmness of the pinna of the ear
• Decreased immature lanugo hair over the back
• Decreasing opacity of the skin

Question 4

1st day assessment

Neurologic criteria

Answer 4

Increasing flexion of legs, hips and arms
Increasing tone of flexor muscles of the neck
Decreasing laxity of the joints

Question 5

Physiologic anemia

Answer 5

Noted at 2-3 months of age in term infants and 1-2 months in preterm infants.
From increased tissue oxygenation experienced at birth, shortened RBC span, low EPO level

Question 6

Jaundice why?

Answer 6

Newborns have much greater rate of bilirubin production due to increased hematocrit and shorter RBC lifespan (70-90 days).
Jaundice on the 1st day of life is ALWAYS pathologic = hemolysis, internal hemorrhage or infection.

Question 7

Etiology of indirect unconjugated hyperbilirubinemia (5)

Answer 7

1. Hemolysis: blood group incompability, RBC enzyme defects, thalassemia
2. Physiologic jaundice: A diagnose of exclusion. Pathologic if it is clinically evident in the 1st day of life
3. Crigler - Najjar syndrome: Serious, rare AR disorder. Deficiency of glucoronosyltransferase
4. Gilbert: Mutation of glucuronosyltransferase
5. Breast milk jaundice - breast milk contains an inhibitor of bilirubin conjugation

Question 8

Treatment

Answer 8

1. Phototherapy: photochemical reaction producing a more water soluble form of bilirubin
2. Exchange transfusion: for very high level of bilirubin

Question 9

Etiology direct conjugated hyperbilirubinemia

Answer 9

Direct > 2mg/dL is never physiologic! 
It is not neurotoxic but signifies a serious underlying disorder. 
1. CMV
2. TORCH
3. Neonatal hepatitis 
4. Sepsis
5. CF
6. Biliary atresia: presence of dark urine and gray stool with jaundice after 2 week of life

Question 10

Kernicterus etiology

Answer 10

Results when indirect bilirubin is deposited in brain cells and disrupts neonatal metabolism and function, especially in the basal ganglia.

Question 11

Kernicterus symptoms

Answer 11

Lethargy, hypotonia, irritability, poor Moro reflex, poor feeding
- Tx: exchange transfusion
Later signs: pulmonary hemorrhage, fever, seizures