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SMALL FOR GESTATIONAL AGE INFANTS (SGA)

Small for gestational age infants are defined as having a birth weight more than 2SD below the

mean or less than the 10th percentile of a population specific weight versus gestational age plot.

TYPES

Symmetric:  Weight, head circumference and length all below the 10th percentile. Brain growth may be

limited.

Causes

  intrinsic fetal causes

  intrauterine infection

  severe placental insufficiency

  constitutionally small infant

Asymmetric: Weight below the 10th percentile but head circumference and length relatively preserved.

Brain growth relatively spared.

Causes

  interference with placental function or maternal health in 3rd trimester.

  Infants whose weight is greater than the 10th percentile but who are thin relative to their length

and head circumference are at similar risk of neonatal complications as SGA infants. They should

be considered "relatively" SGA (Clifford syndrome).

  The weight/length ratio (or the Ponderal Index = [weight (g)]/[length (cm)]3 ) is less than normal

for such infants. However, unless great care is taken with the measurement of length the

calculated index can be misleading.

AETIOLOGY

FETAL

  chromosome disorders (eg Trisomy 21, Trisomy 18)

  chronic fetal infection (eg CMV, Rubella, Syphilis, Toxoplasmosis)

  congenital malformations: including congenital heart disease, diaphragmatic hernia, tracheo-

oesophageal fistula

  syndrome complex

  radiation

  multiple gestation relates more to placental limitation rather than intrinsic baby problem

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MOTHER

  pregnancy induced hypertension

  hypertension or renal disease or both

  hypoxaemia (high altitude, cyanotic cardiac or pulmonary disease)

  malnutrition or chronic illness  drugs (narcotics, alcohol, cigarettes, cocaine, antimetabolites)

PLACENTAL

  decreased placental weight or cellularity or both

  decrease in surface area, infarction

  villous placentitis (bacterial, viral, parasitic)

  tumour (chorioangioma, hydatiform mole)

  placental separation

  twin to twin transfusion syndrome

CONSTITUTIONAL

  familial and racial background

PHYSICAL EXAMINATION

Physical examination of the SGA infant must include a detailed search for associated abnormalities.

  dysmorphic features "unusual" facies

  abnormal hands and feet

  abnormal palmar creases

  in addition to gross anomalies

  ocular disorders, such as

  cataracts

  cloudy cornea

  chorioretinitis

  features of intrauterine infection

  hepatosplenomegaly

   jaundice

  blueberry-muffin rash

PROBLEMS IN SGA

Problem Pathogenesis

Intrauterine fetal demise Hypoxia, acidosis, infection and lethal anomaly

Perinatal asphyxia Decreased uteroplacental perfusion in labour

chronic fetal hypoxia-acidosis

Hypoglycemia Decreased tissue glycogen stores, decreased gluconeogenesis and

high glucose requirements

Polycythemia -hyperviscosity fetal hypoxia with increased erythropoietin production

Hypothermia Large surface area, poor subcutaneous fat stores

Respiratory distress intrauterine pneumonia, meconium aspiration syndrome, PPHN

Investigations are required to:

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  screen for hypoglycemia

  assess the infant according to clinical signs

  polycythemia and hypocalcaemia are more common.

  if respiratory distress present, ABG and Chest X-ray.

  establish the cause of growth restriction

  intrauterine infection suspected; check maternal TORCH serology and screen infant urine and

saliva for CMV (further investigation will be required if suspicion confirmed).

  if dysmorphic; genetic consultation and chromosome studies

  if showing signs of withdrawal urine for drug screen.

  ultrasonography and echocardiography, if clinically indicated

MANAGEMENT

At Delivery: Place promptly under a radiant warmer and dry. Infants with severe SGA, particularly in

association with fetal distress, are at risk of aspiration of meconium , hypoxaemia, hypotension, mixed

metabolic and respiratory acidosis and persistent pulmonary hypertension.

Hypothermia: Nurse in a thermoneutral environment

Hypoglycemia:  Monitor blood glucose and commence early enteral feeds or intravenous glucose

infusion.

Necrotisingenterocolitis: Infants, particularly preterm SGA, found to have placental insufficiency and

abnormal umbilical artery Doppler studies may be at particular risk of developing NEC or gastrointestinal

perforation. Enteral feeding should be increased gradually.

Polycythemia:  Partial volume exchange may be required for symptomatic infants.

OUTCOME

Principally determined by the cause.

Postnatal physical growth:

  Symmetric SGA - smaller and relatively under weight throughout life.

  Asymmetric SGA - accelerated velocity of growth ("catch up growth") in first 6 months and

normal development.

Neurodevelopmental outcome:

  Term SGA - no increase risk of severe neurologic morbidity compared to term AGA infants.

However increased hyperactivity, short attention span and learning problems

  Preterm SGA - Minor neurologic abnormalities more common than in preterm AGA infants.