Introduction

Small for gestational age (SGA) babies are those weighing ≤2500 g if born at term. They fall into two groups:

• Babies whose growth at all gestational ages has been low. They are light-for-dates, but otherwise healthy.
• Growth is normal in the early part of pregnancy, but slows in utero by at least two measurements, normally ultrasound. This is due to intrauterine growth restriction (IUGR). They have a wasted appearance with little subcutaneous fat. They are at greater risk of dying.

The very low birth weight (VLBW) baby weighs ≤1500 g.

Significance of SGA

SGA fetuses are at greater risk of:

• Stillbirth.
• Intrapartum hypoxia.
• Neonatal complications.
• Impaired neurodevelopment.
• Possibly type 2 (non-insulin-dependent) diabetes and hypertension in adult life.^[1]

The majority of term SGA infants have no immediate appreciable morbidity or mortality.

Epidemiology

Incidence

Approximately 9% of neonates are of low birth weight - ie less than 2,500 g.^[2] Of these, approximately 25% are preterm and 85% are small for gestational age.

Risk factors

• Maternal age ≤17 years or ≥35 years.
• Socio-economic class IV or V.^[3]
• Weight before pregnancy ≤50 kg or ≥75 kg.^[4]
• Smoking^[5] - although quitting before 15 weeks of gestation may negate risk.^[6]
• Excessive consumption of alcohol.
• Drug/substance abuse.
• Previous low birth weight baby.
• Anaemia in pregnancy.
• Chronic hypertensive disease.^[7]
• Maternal polycystic ovarian syndrome.^[8]
• Antepartum haemorrhage.
• Multiple pregnancy.
• Congenital fetal defects.
• Intrauterine infection.

Diagnosis

There is a variety of methods used to detect SGA fetuses:

• Abdominal palpation (the least accurate).
• Measurement of symphyseal fundal height.
• Ultrasound - estimated fetal weight.
• Ultrasound - biophysical profiling.
• Ultrasound - Doppler flow velocimetry.

However, the following should not be forgotten:

• Most investigations use a one-off measurement (size) to predict SGA, while there is evidence that it is the trend (growth) that is of more value in predicting poor fetal outcome.
• All require an accurate estimation of gestation as a prerequisite for accuracy.
• Most tests diagnose SGA fetuses, rather than growth-restricted fetuses.
• Little allowance is made for important prognostic factors for SGA, such as maternal height, weight, ethnicity, parity and fetal gender.

Management

Antenatal

• If an SGA fetus is found, there should be a careful ultrasound survey for chromosome defects. Karyotyping may be offered.^[9]
• The fetus should be monitored with umbilical artery Doppler. A study comparing fetal heart rate monitoring, biophysical profile and umbilical artery Doppler found that only umbilical artery Doppler had value in predicting poor perinatal outcomes in SGA fetuses.^[10] Absent or reversed end diastolic flow is associated with increased perinatal mortality and morbidity.^[11]
• Timing delivery is a balance between Doppler findings and gestation. If the fetus is less than 36 weeks of gestation, the mother should receive corticosteroids.
• The fetus should be delivered in a unit with neonatal expertise and facilities.

Intrapartum

• Continuous electronic fetal monitoring should be offered.^[12]
• There is currently no evidence to support immediate delivery.^[13][14]

Post-delivery

Care should either be provided for in a nursery at a temperature greater than 24°C or, for very small babies, in an incubator at a temperature of 26-32°C and humidity 65-75%.

Temperature is decided by monitoring the infant's core temperature and adjusting accordingly.

Oxygen is supplied either by a head box or into the incubator:

• The level is adjusted according to monitoring by transcutaneous oxygen electrode or pulse oximetry.
• A level is maintained that avoids hypoxia, but also considers the problem of toxicity on the retina (retinopathy of prematurity (ROP)).^[15]

Infection control is important:

• Careful attention should be paid to avoiding overcrowding and the possibility of medical attendants or relatives introducing infection into the nursery.
• Hands must be washed before handling a baby.

Feeding should start six hours after birth, using breast milk as soon as possible:

• Normally, the baby is fed by nasogastric tube or spoon.
• They are put to the breast as soon as they are suckling strongly.
• If the baby is unable to accept enteral feeding then supplemental parenteral nutrition may be needed.
• Regularly check for hypoglycaemia and treat with IV glucose if necessary.

Supplements of vitamin A, C, D, niacin and riboflavin are also given.

If Ca²⁺ <2 mmol/L, give calcium gluconate IV slowly.

Cranial ultrasound (to detect haemorrhage).

Complications

• Spontaneous preterm delivery.^[16]
• Respiratory distress syndrome.
• Cyanotic attacks - caused either by inadequate ventilation or cerebral damage.
• Jaundice.
• Hypoglycaemia - affects 15% of cases.
• Hypocalcaemia - usually occurs in the first 24 hours of life.
• Intracranial haemorrhage - mainly occurs in babies weighing <1500 g.
• Retinopathy of prematurity and sequelae.^[15]
• Cerebral palsy.^[17]

Prognosis

• Mortality increases with decreasing weight.
• Preterm, low birth weight infants have an extremely high risk of mortality in their first year and parents should be counselled regarding this risk.^[18]

Very low birth weight (VLBW) females catch up in growth by 20 years of age, whereas VLBW males remain significantly shorter and lighter than controls.^[19]

Morbidity

See separate article Premature Babies and their Problems.