OVERVIEW

What is a small for gestational age infant?

A small for gestational age (SGA) infant refers to a newborn whose birth weight is below the 10th percentile for their gestational age.

This means the baby's birth weight is lighter than 90% of other newborns of the same gestational age. In other words, the child is among the smallest 10% in weight for babies born at that gestational age.

Is SGA common?

Yes. Approximately 9%–10% of newborns are small for gestational age.

Do SGA infants require treatment?

SGA infants fall into two categories:

• Constitutionally small infants: Their small size is determined by genetic factors, and their growth and development follow a normal pattern. No underlying disease exists, and no additional treatment is needed.

• Growth-restricted infants: Their intrauterine growth is limited due to pathological factors (intrauterine growth restriction, IUGR). These cases require close monitoring during pregnancy and after birth, and treatment may be necessary.

• If fetal growth restriction is detected during pregnancy, maternal contributing factors should be identified and addressed to support the baby's development in the womb.

• At delivery, an experienced medical team should perform neonatal resuscitation to ensure the baby's survival.

• Low birth weight infants may develop certain complications after birth, which require prompt treatment if they occur.

What are the types of SGA infants?

They can be broadly classified into two types based on body proportions at birth: symmetrical and asymmetrical.

• Symmetrical SGA: Growth restriction likely occurs in early pregnancy due to causes like intrauterine infections or chromosomal abnormalities. These infants have proportionally small head circumference and weight, and their brain development may also be affected.

• Asymmetrical SGA: Growth restriction typically occurs in late pregnancy due to maternal malnutrition, hypertension, etc. These infants have low weight but normal head circumference, appearing "head-sparing" with a relatively large head and thin body. Medically, this type is considered less likely to affect brain development.

SYMPTOMS

What are the manifestations of small for gestational age infants?

The most obvious manifestations are low birth weight, thin body shape, reduced subcutaneous fat, wrinkled skin, and poor elasticity.

They may also exhibit symptoms such as cyanosis after birth, inability to feed, lack of crying, and low body temperature, which often indicate complications.

What complications might small for gestational age infants experience at birth?

• Neonatal hypoglycemia: Due to insufficient nutrient storage in the body, they are prone to hypoglycemia.

• Premature birth: Infants with intrauterine growth restriction are at risk of premature birth.

• Perinatal hypoxia and asphyxia: Small for gestational age infants may experience hypoxia in the womb and asphyxia after birth.

• Polycythemia: Due to intrauterine hypoxia, these infants often develop excess red blood cells.

• Hypothermia: With reduced fat tissue and weak thermoregulation, they are prone to hypothermia.

• Meconium aspiration syndrome: Hypoxia increases the risk of meconium aspiration.

• Perinatal death: The mortality rate of small for gestational age infants during the perinatal period (from 28 weeks of pregnancy to 1 week after birth) is higher than that of normal fetuses/newborns. Asphyxia after birth and congenital malformations are the main causes of death.

What sequelae may small for gestational age infants experience?

The presence of sequelae in small for gestational age infants depends on whether intrauterine growth restriction was caused by disease factors.

• Most small for gestational age infants can achieve catch-up growth within 2 years after birth, with physical and intellectual development reaching normal standards.

• A small proportion may experience lifelong growth retardation, cognitive impairment, motor dysfunction, cerebral palsy, and other sequelae.

CAUSES

What are the common causes of small for gestational age infants?

• Maternal hypertension during pregnancy is a common cause of small for gestational age infants.

• Severe nutritional deficiency in the mother during pregnancy may also lead to a smaller fetus.

• Abnormal uterine environment, including placental or umbilical cord abnormalities and uterine malformations, can cause delayed fetal growth.

• Congenital developmental abnormalities, including chromosomal abnormalities and organ structural malformations, may restrict fetal growth.

• Genetic factors can also increase the likelihood of small for gestational age infants. For example, if parents have a small physique, the child may also be small.

DIAGNOSIS

How is small for gestational age diagnosed?

During pregnancy, color ultrasound can estimate fetal weight and compare it with gestational age to initially determine if the fetus is small for gestational age.

After birth, the baby's birth weight and gestational age can be compared with statistical data tables to diagnose whether the baby is small for gestational age.

What tests should the mother undergo for a small-for-gestational-age baby?

If the fetus is found to be small for gestational age during pregnancy, the mother should undergo comprehensive tests and evaluations.

• Fetal color ultrasound: Depending on the condition, perform fetal color ultrasound every 1–4 weeks to assess fetal growth rate and evaluate the uterus, amniotic fluid, and placenta.

• Fetal movement and heart rate monitoring: The mother should monitor fetal movements and undergo regular fetal heart rate monitoring to dynamically assess the fetus's condition.

• Umbilical artery Doppler examination: This test measures umbilical artery blood flow velocity to evaluate whether the fetus is experiencing intrauterine hypoxia. If the Doppler shows absent or reversed umbilical artery blood flow, it may indicate fetal hypoxia, and delivery may need to be considered.

• Hypertension screening: The mother should also undergo tests for gestational hypertension, including blood pressure measurement, urinalysis, and biochemical tests.

• Fetal karyotype testing: If the small-for-gestational-age condition occurs in early pregnancy (before 24 weeks) or if ultrasound reveals significant developmental abnormalities, fetal karyotype testing may be performed to rule out serious genetic disorders such as Down syndrome or Edwards syndrome.

• Intrauterine infection screening: Intrauterine infections (e.g., cytomegalovirus, varicella, toxoplasmosis, rubella) can also cause fetal growth restriction and should be ruled out.

What tests should a small-for-gestational-age newborn undergo?

Depending on symptoms, the baby may need physical examinations, blood glucose tests, blood gas analysis, complete blood count (CBC), biochemical tests, chest X-rays, or head MRI.

• Physical examination: Assess for developmental abnormalities.

• Blood glucose monitoring: Small-for-gestational-age babies are prone to hypoglycemia, requiring regular monitoring.

• Blood gas analysis: If the baby shows cyanosis, this test helps detect hypoxia or acidosis.

• CBC: Check for polycythemia.

• Biochemical tests: Evaluate liver and kidney function and electrolyte levels.

• Chest X-ray: If the baby has rapid breathing, this test can detect meconium aspiration or respiratory distress syndrome.

• Head MRI: If the baby experiences asphyxia, an MRI can assess brain damage.

What should be noted when testing a small-for-gestational-age baby?

An MRI may require sedation. Under medical guidance, sedation is safe, and the drugs used are quickly eliminated from the baby's body. Parents should not delay necessary tests or treatments due to excessive concern about sedation side effects.

TREATMENT

Can small for gestational age babies be delivered vaginally?

Small for gestational age babies can attempt vaginal delivery.

However, if the fetus shows signs of intrauterine hypoxia, including abnormal fetal heart monitoring or abnormal umbilical blood flow, then the baby should be delivered as soon as possible to reduce hypoxia-related damage. In some cases, a cesarean section may be necessary.

Which department should small for gestational age babies see?

If fetal growth restriction is detected during pregnancy, the mother should visit the obstetrics department.

After birth, if complications arise, small for gestational age babies may need treatment in the neonatology department or neonatal intensive care unit (NICU).

How are small for gestational age babies treated?

Small for gestational age babies who had a smooth delivery, no asphyxia, no postnatal symptoms, and relatively higher birth weight may not require treatment in the neonatology department or NICU. After blood glucose monitoring, they can stay with their mothers in the same room for care. However, attention should be paid to keeping them warm and initiating breastfeeding early. If symptoms such as refusal to feed, cyanosis, or low body temperature are observed, prompt pediatric consultation is needed to assess for complications. Severe complications may require hospitalization.

If the baby's birth weight is too low, or if there is postnatal asphyxia or complications, treatment in the neonatology department or NICU may be necessary.

What should be noted during hospitalization for small for gestational age babies?

If admitted to a non-accompanied ward, family members should encourage the mother to pump breast milk regularly (which can be stored in breast milk storage bags and kept in the refrigerator) to maintain sufficient milk supply. This ensures the baby can still receive breast milk after discharge, which is highly beneficial for long-term health. If permitted by the neonatal ward, expressed breast milk can also be provided to the baby during hospitalization to allow for breastfeeding.

DIET & LIFESTYLE

What should small-for-gestational-age infants pay attention to in their diet?

Breastfeeding is recommended, with early initiation and frequent suckling. This can meet the child's nutritional needs, prevent hypoglycemia, and also promote breast milk production.

What should small-for-gestational-age infants pay attention to in daily life?

Maintain warmth and ensure adequate feeding. Small-for-gestational-age infants are prone to hypothermia, so timely warmth is essential. Start feeding as early as possible. If the child has weak sucking ability and cannot feed properly, seek medical help promptly.

PREVENTION

How to prevent small for gestational age infants?

• During pregnancy, mothers should maintain a balanced diet, including staple foods, meat, eggs, dairy, vegetables, and fruits, to ensure normal weight gain.

• Attend regular prenatal checkups. Ultrasound examinations can help detect early signs of fetal weight below the gestational age, allowing timely intervention.

• If the fetus shows signs of intrauterine hypoxia, follow the doctor's advice to terminate the pregnancy and deliver the baby to reduce the duration of fetal hypoxia.

If a mother has previously given birth to a small for gestational age infant, is she more likely to have another? How to prevent it?

Mothers who have previously delivered a small for gestational age infant may have a higher chance of another in subsequent pregnancies. They should quit smoking and alcohol, ensure balanced and adequate nutrition, attend regular prenatal checkups, and those with a history of gestational hypertension should monitor blood pressure changes closely.