SGA

• Small for gestational age is defined as a fetus that measures below the 10th centile for their gestational age. Two measurements on ultrasound are used to assess the fetal size:

  • Estimated fetal weight (EFW)
  • Fetal abdominal circumference (AC)
• Severe SGA:

  • Fetus is below the 3rd centile for their gestational age
• Low birth weight:

  • Defined as a birth weight of less than 2500g (2.5kg)
• Causes of SGA can be divided into 2 categories:

  • Constitutionally small - matching the mother and others in the family, and growing appropriately on the growth chart
  • Fetal growth restriction, also known as intrauterine growth restriction = small fetus, or fetus not growing as expected, due to pathology
• The causes of fetal growth restriction can be divided into two categories:

  • Placenta mediated growth restriction
  • Non-placenta mediated growth restriction, where the baby is small due to a genetic or structural abnormality
• Causes of placenta mediated growth restriction (transfer of nutrients across placenta):

  • Idiopathic
  • Pre-eclampsia
  • Maternal smoking or alcohol
  • Anaemia
  • Malnutrition
  • Infection
  • Maternal health conditions
• Non-placenta medicated growth restriction refers to pathology of the fetus, such as:

  • Genetic abnormalities
  • Structural abnormalities
  • Fetal infection
  • Errors of metabolism
• There may be other signs that would indicate FGR other than the fetus being SGA, such as:

  • Reduced amniotic fluid volume (oligohydramnios)
  • Abnormal Doppler studies
  • Reduced fetal movements
  • Abnormal CTGs
• Short term complications of fetal growth restriction include:

  • Fetal death or stillbirth
  • Birth asphyxia
  • Neonatal hypothermia
  • Neonatal hypoglycaemia
• Growth restricted babies have a long term increased risk of:

  • Cardiovascular disease, particularly hypertension
  • Type 2 diabetes
  • Obesity
  • Mood and behavioural problems
• Risk factors for SGA:

  • Previous SGA baby
  • Obesity
  • Smoking
  • Diabetes
  • Existing hypertension
  • Pre-eclampsia
  • Increased maternal age >35
  • Multiple pregnancy
  • Low PAPPA
  • Antepartum haemorrhage
  • Antiphospholipid syndrome
• The RCOG green-top guidelines on SGA (2013) lists major and minor risk factors. At the booking clinic, women are assessed for risk factors for SGA.
• Low-risk women have monitoring of the symphysis fundal height (SFH) at every antenatal appointment from 24 weeks onwards to identify potential SGA. The SFH is plotted on a customised growth chart to assess the appropriate size for the individual woman. If the symphysis fundal height is less than the 10th centile, women are booked for serial growth scans with umbilical artery doppler.
• Women are booked for serial growth scans with umbilical artery doppler if they have:

  • Three or more minor risk factors
  • One or more major risk factors
  • Issues with measuring the symphysis fundal height (e.g. large fibroids or BMI > 35)
• Women at risk or with SGA are monitored closely with serial ultrasound scans measuring:

  • Estimated fetal weight (EFW) and abdominal circumference (AC) to determine the growth velocity
  • Umbilical arterial pulsatility index (UA-PI) to measure flow through the umbilical artery
  • Amniotic fluid volume
• Management:

  • Identify those at risk of SGA
  • Aspirin is given to those at risk of pre-eclampsia
  • Treating modifiable risk factors e.g. stop smoking
  • Serial growth scans to monitor growth
  • Early delivery where growth is static, or there are other concerns
• When a fetus is identified as SGA, investigations to identify the underlying cause include:

  • Blood pressure and urine dipstick for pre-eclampsia
  • Uterine artery doppler scanning
  • Detailed fetal anatomy scan by fetal medicine
  • Karyotyping for chromosomal abnormalities
  • Testing for infections (e.g. toxoplasmosis, cytomegalovirus, syphilis and malaria)
• Corticosteroids are given when delivery is planned early, particularly when delivered by caesarean section - to reduce risk of respiratory distress syndrome