Small for gestational age

Small for gestational age
Classification and external resources
G a baby is not the definition of small DiseasesDB = 31952
ICD-10	P05, P07
ICD-9	764, 765
MeSH	D007230

Small for gestational age (SGA) babies are those who are smaller in size than normal for the gestational age, most commonly defined as a weight below the 10th percentile for the gestational age.

Terminology

Not all fetuses that are SGA are pathologically growth restricted and, in fact, may be constitutionally small. If small for gestational age babies have been the subject of intrauterine growth restriction (IUGR), formerly known as intrauterine growth retardation, the term SGA associated with IUGR is used. Intrauterine growth restriction (IUGR) refers to a condition in which a fetus is unable to achieve its genetically determined potential size. This functional definition seeks to identify a population of fetuses at risk for modifiable but otherwise poor outcomes. This definition intentionally excludes fetuses that are small for gestational age (SGA) but are not pathologically small

A related term is Low birth weight (LBW), defined as an infant with a birth weight (that is, mass at the time of birth) of less than 2500 g (5 lb 8 oz), regardless of gestational age at the time of birth. Related definitions include Very Low Birth Weight (VLBW) which is less than 1500 g, and Extremely Low Birth Weight (ELBW) which is less than 1000 g. Normal Weight at term delivery is 2500 g - 4200 g.

SGA is not a synonym of LBW, VLBW or ELBW. Example: 35 week gestational age delivery, 2250g weight is appropriate for gestational age but is still LBW. One third of low-birth-weight neonates - infants weighing less than 2500g - are small for gestational age.

There is a 8.1% incidence of low birth weight in developed countries, and 6–30% in developing countries. Much of this can be attributed to the health of the mother during pregnancy. One third of babies born with a low birth weight are also small for gestational age.

Maternal serum of Vitamin D (25-OH) are associated with SGA.

Diagnosis

The condition is determined by birth weight and/or length.

A related condition, IUGR, is generally diagnosed by measuring the mother's uterus, with the fundal height being less than it should be for that stage of the pregnancy. If it is suspected, the mother will usually be sent for an ultrasound to confirm.

Predetermining factors

Not all fetuses that are SGA are pathologically growth restricted and, in fact, may be constitutionally small.

The risk factors for and etiologies of pathological SGA can be broadly divided into 3 categories-

• Fetal
• Maternal
• Placental

The primary risk factor is that development of the placenta is insufficient to meet the demands of the fetus, resulting in malnutrition of the developing fetus. There are numerous contributing factors of both environmental and genetic origin:

• Environmental factors such as poor nutrition, maternal tobacco smoking, drug addiction or alcoholism
• Severe anaemia (although hydrops may also occur)
• Thrombophilia (tendency for thrombosis)
• Prolonged pregnancy
• Pre-eclampsia
• Chromosomal abnormalities
• Diabetes Mellitus
• Connective Tissue Disease/Disorders (Systemic Lupus Erythematosis), Ehlers-Danlos Syndrome
• Damaged or reduced placental tissue due to:
  • Chronic renal failure
  • Sickle cell anemia
  • Phenylketonuria
• Infections such as rubella, cytomegalovirus, toxoplasmosis or syphilis
• Twins and multiple births.

Categories of growth restriction

There are two distinct categories of growth restriction, indicating the stage at which the development was slowed. Small for gestational age babies can be classified as having symmetrical or asymmetrical growth restriction. Some conditions are associated with both symmetrical and asymmetrical growth restriction.

Symmetrical

Symmetrical growth restriction, less commonly known as global growth restriction, indicates that the fetus has developed slowly throughout the duration of the pregnancy and was thus affected from a very early stage. The head circumference of such a newborn is in proportion to the rest of the body. Common causes include:

• Early intrauterine infections, such as cytomegalovirus, rubella or toxoplasmosis
• Chromosomal abnormalities
• Anemia
• Maternal substance abuse (prenatal alcohol use can result in Fetal alcohol syndrome)

Asymmetrical

Asymmetrical growth restriction occurs when the head grows at a normal or slightly reduced rate but the body grows at a much slower rate. Such babies have a disparity in their length and head circumference when compared to the birth weight, hence the term "asymmetrical." In these cases, the embryo/fetus has grown normally for the first two trimesters but encounters difficulties in the third, usually secondary to pre-eclampsia. A lack of subcutaneous fat leads to a thin and small body out of proportion with the head. Other symptoms include dry, peeling skin and an overly-thin umbilical cord. The baby is at increased risk of hypoxia and hypoglycaemia.

Causes include:

• Chronic high blood pressure
• Severe malnutrition
• Genetic mutations, Ehlers–Danlos syndrome

Treatment

90 percent of babies born SGA catch up in growth by the age of 2. However, all SGA babies should be watched for signs of Failure-to-Thrive (FTT), hypoglycemia and other conditions common to SGA babies (see below). Hypoglycemia is common in asymmetrical SGA babies because their larger brains burn calories at a faster rate than their usually limited fat stores hold. Hypoglycemia is treated by frequent feedings and/or additions of cornstarch-based products (such as Duocal powder) to the feedings.

For the 10 percent of those that are SGA without catchup growth by the age of 2, an endocrinologist should be consulted. Some cases warrant growth hormone therapy (GHT).

There are some common conditions and disorders found in many that are SGA (and especially those that are SGA without catchup growth by age 2). They should be treated by the appropriate specialist:

• Gastroenterologist - for gastrointestinal issues such as: reflux (GERD) and/or delayed gastric emptying (DGE)
• Dietitian - to address caloric deficits. Dietitians are usually brought in for cases that include FTT
• Speech Language Pathologist (SLP) or Occupational Therapist (OT) - for feeding issues. OTs may also treat sensory issues
• Behaviorist - for feeding issues, a behavioral approach may also be used, but usually for older children (over 2)
• Allergist - to diagnose or rule out food allergies (not necessarily more common in those SGA than the normal population)
• Ear, Nose and Throat doctor (ENT) - to diagnose enlarged adenoids or tonsils (not necessarily more common in those SGA than the normal population)

For IUGR (during pregnancy), possible treatments include the early induction of labor, though this is only done if the condition has been diagnosed and seen as a risk to the health of the fetus.