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Small for gestational age
Graph showing which babies fit the definition of small. (DiseaseDB #31952)
Specialty	Pediatrics

Small for gestational age (SGA) newborns are those who are smaller in size than normal for thegestational age. SGA is most commonly defined as a weight below the 10thpercentile for the gestational age.^[1] SGA predicts susceptibility tohypoglycemia,hypothermia, andpolycythemia.^[2] By definition, at least 10% of all newborns will be labeled SGA. All SGA babies should be watched for signs offailure to thrive, hypoglycemia, and other health conditions.

Being small for gestational age is broadly either:^[3]

• Being constitutionally small, or caused by agenetic trait of the baby
• Intrauterine growth restriction, also called pathological SGA

The condition is defined by birth weight and/or length.^{[citation needed]}

Intrauterine growth restriction is generally diagnosed by measuring the mother'suterus, with thefundal height being less than it should be for that stage of the pregnancy. If it is suspected, the mother will usually be sent for anultrasound to confirm.^{[citation needed]}

There are numerous Single Nucleotide Polymorphisms (SNPs), or other genetic mutations, that increase the risk of having a small for gestational age baby.^[4]

Ninety percent of babies born SGA catch up in growth by the time they reach two years old. For the ten percent of those without catch-up growth by two years old, an endocrinologist should be consulted. Some cases warrantgrowth hormone therapy.^{[citation needed]}

Hypoglycemia is common in asymmetrical SGA babies because their larger brains burn calories at a faster rate than their usually limited fat stores can hold. Hypoglycemia is treated by frequent feedings and/or additions of cornstarch-based products (such as Duocal powder) to the feedings.^{[citation needed]}

Some common conditions and disorders are found in many babies who are SGA (and especially those without catch-up growth by two years old).^{[citation needed]}

• Gastroenterologist – for gastrointestinal issues such as reflux and/or delayed gastric emptying
• Dietitian – to address caloric deficits. Dietitians are usually brought in for cases that include failure to thrive. According to the theory ofthrifty phenotype, causes of growth restriction also triggerepigenetic responses in the fetus that are otherwise activated in times of chronic food shortage, and if the offspring develops in an environment rich in food, it may be more prone to metabolic disorders such asobesity andtype II diabetes.^[5]
• Speech-language pathologist oroccupational therapist – occupational therapists 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 – to diagnose enlarged adenoids or tonsils (not necessarily more common in those SGA than the normal population)

For intrauterine growth restriction (during pregnancy), possible treatments include the earlyinduction of labor, though this is only done if the condition has been diagnosed and seen as a risk to the health of the fetus.^{[citation needed]}

If small for gestational age babies have been the subject of intrauterine growth restriction, formerly known as intrauterine growth retardation,^[6] the term "SGA associated with intrauterine growth restriction" is used.Intrauterine growth restriction 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.^[3] Infants born SGA with severe short stature (or severe SGA) are defined as having a length less than 2.5 standard deviation scores below the mean.^[7]

A related term islow birth weight, defined as aninfant with abirth weight (that is, mass at the time of birth^[8]) of less than 2,500 g (5 lb 8 oz), regardless of gestational age at the time of birth.Other related terms include "very low birth weight", which is less than 1,500 g (3 lb 5 oz); and "extremely low birth weight", which is less than 1,000 g (2 lb 3 oz).^[9] Normal weight at term delivery is 2,500–4,200 g (5 lb 8 oz – 9 lb 4 oz).^{[citation needed]}

SGA is not asynonym of low birth weight, very low birth weight, or extremely low birth weight.For example, with a 35-week gestational age delivery, a weight of 2,250 g (4 lb 15 oz) is appropriate for gestational age but is still low birth weight. One third of low-birth-weight neonates – infants weighing less than 2,500 g (5 lb 8 oz) – are small for gestational age.^{[citation needed]}

There is an 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 themother duringpregnancy. One-third of babies born with a low birth weight are also small for gestational age. Infants that are born at low birth weights are at risk of developingneonatal infection.^{[citation needed]}

Both low and high maternal serum Vitamin D (25-OH) are associated with higher incidence SGA in white women, although the correlation does not seem to hold for African American women.^[10]

• Disorders related to length of gestation and fetal growth
• Neonatology

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