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Small-for-Gestational-Age (SGA) Infant

(Dysmaturity; Intrauterine Growth Restriction)

by James W. Kendig, MD, Ursula Nawab, MD

Infants whose weight is < the 10th percentile for gestational age are classified as small for gestational age (SGA). Complications include perinatal asphyxia, meconium aspiration, and hypoglycemia.

The Fenton growth charts provide a more precise assessment of growth vs gestational age (see Figure: Fenton Growth Chart for Preterm Boys and see Fenton Growth Chart for Preterm Girls).

Etiology

Causes may be divided into those in which the growth restriction is

  • Symmetric: Height, weight, and head circumference are about equally affected.

  • Asymmetric: Weight is most affected, with a relative sparing of growth of the brain, cranium, and long bones.

Symmetric growth restriction usually results from a fetal problem that begins early in gestation, often during the 1st trimester. When the cause begins relatively early in gestation, all of the body is affected, resulting in fewer cells of all types. Common causes include

  • Many genetic disorders

  • First-trimester congenital infections (eg, with cytomegalovirus, rubella virus, or Toxoplasma gondii)

Asymmetric growth restriction usually results from placental or maternal problems that typically manifest in the late 2nd or the 3rd trimester. When the cause begins relatively late in gestation, organs and tissues are not equally affected, resulting in asymmetric growth restriction. Common causes include

  • Placental insufficiency resulting from maternal disease involving the small blood vessels (eg, preeclampsia [see Preeclampsia and Eclampsia], hypertension [see Hypertension in Pregnancy], renal disease [see Renal Insufficiency in Pregnancy], antiphospholipid antibody syndrome [see Antiphospholipid Antibody Syndrome], long-standing diabetes)

  • Relative placental insufficiency caused by multiple gestation

  • Placental involution accompanying postmaturity

  • Chronic maternal hypoxemia caused by pulmonary or cardiac disease

  • Maternal malnutrition

  • Conception using assisted reproductive technology

An infant may also have asymmetric growth restriction and be small for gestational age (SGA—see Small-for-Gestational-Age (SGA) Infant) if the mother is a heavy user of opioids, cocaine, alcohol, and/or tobacco during pregnancy.

Symptoms and Signs

Despite their size, SGA infants have physical characteristics (eg, skin appearance, ear cartilage, sole creases) and behavior (eg, alertness, spontaneous activity, zest for feeding) similar to those of normal-sized infants of like gestational age. However, they may appear thin with decreased muscle mass and subcutaneous fat tissue. Facial features may appear sunken, resembling those of an elderly person ("wizened facies"). The umbilical cord can appear thin and small.

Complications

Full-term SGA infants do not have the complications related to organ system immaturity that premature infants of similar size have. They are, however, at risk of

  • Perinatal asphyxia

  • Meconium aspiration

  • Hypoglycemia

  • Hypothermia

Perinatal asphyxia during labor is the most serious potential complication. It is a risk if intrauterine growth restriction is caused by placental insufficiency (with marginally adequate placental perfusion) because each uterine contraction slows or stops maternal placental perfusion by compressing the spiral arteries. Therefore, when placental insufficiency is suspected, the fetus should be assessed before labor and the fetal heart rate should be monitored during labor. If fetal compromise is detected, rapid delivery, often by cesarean delivery, is indicated.

Meconium aspiration may occur during perinatal asphyxia. SGA infants, especially those who are postmature, may pass meconium into the amniotic sac and begin deep gasping movements. The consequent aspiration is likely to result in meconium aspiration syndrome (often most severe in growth-restricted or postmature infants, because the meconium is contained in a smaller volume of amniotic fluid and thus more concentrated—see Meconium Aspiration Syndrome).

Hypoglycemia often occurs in the early hours and days of life because of a lack of adequate glycogen synthesis and thus decreased glycogen stores and must be treated quickly with IV glucose (see Neonatal Hypoglycemia).

Polycythemia (see Perinatal Polycythemia and Hyperviscosity Syndrome) may occur when SGA fetuses experience chronic mild hypoxia caused by placental insufficiency. Erythropoietin release is increased, leading to an increased rate of erythrocyte production. The neonate with polycythemia at birth appears ruddy and may be tachypneic or lethargic.

Hypothermia (see Hypothermia in Neonates) may occur because of impaired thermoregulation, which involves multiple factors including increased heat loss due to the decrease in subcutaneous fat, decreased heat production due to intrauterine stress and depletion of nutrient stores, and increased surface to volume ratio due to small size. SGA infants should be in a thermoneutral environment to minimize O 2 consumption.


Prognosis

If asphyxia can be avoided, neurologic prognosis for term SGA infants is quite good. However, later in life there is probably increased risk of ischemic heart disease, hypertension, and stroke, which are thought to be caused by abnormal vascular development.

Infants who are SGA because of genetic factors, congenital infection, or maternal drug use often have a worse prognosis, depending on the specific diagnosis. If intrauterine growth restriction is caused by chronic placental insufficiency, adequate nutrition may allow SGA infants to demonstrate remarkable “catch-up” growth after delivery.

Treatment

  • Supportive care

Underlying conditions and complications are treated. There is no specific intervention for the SGA state, but prevention is aided by prenatal advice on the importance of avoiding alcohol, tobacco, and illicit drugs.

Key Points

  • Infants whose weight is < the 10th percentile for gestational age are small for gestational age (SGA).

  • Disorders early in gestation cause symmetric growth restriction, in which height, weight, and head circumference are about equally affected.

  • Disorders late in gestation cause asymmetric growth restriction, in which weight is most affected, with relatively normal growth of the brain, cranium, and long bones.

  • Although small, SGA infants do not have the complications related to organ system immaturity that premature infants of similar size have.

  • Complications are mainly those of the underlying cause but generally also include perinatal asphyxia, meconium aspiration, hypoglycemia, polycythemia, and hypothermia.

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