Small for Gestational Age Flashcards
What is small for gestational age?
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)
What is severe SGA?
Low birth weight?
Severe SGA is when the fetus is below the 3rd centile for their gestational age. Low birth weight is defined as a birth weight of less than 2500g.
Causes of SGA?
The causes of SGA can be divided into two categories:
1 - Constitutionally small, matching the mother and others in the family, and growing appropriately on the growth chart
2 - Fetal growth restriction (FGR), also known as intrauterine growth restriction (IUGR)
Fetal growth restriction (FGR), also known as intrauterine growth restriction (IUGR), is when there is a small fetus (or a fetus that is not growing as expected) due to a pathology reducing the amount of nutrients and oxygen being delivered to the fetus through the placenta.
TOM TIP: It is important to note the difference between small for gestational age (SGA) and fetal growth restriction (FGR). Small for gestational age simply means that the baby is small for the dates, without stating why. The fetus may be constitutionally small, growing appropriately, and not at increased risk of complications. Alternatively, the fetus may be small for gestational age due to pathology (i.e. FGR), with a higher risk of morbidity and mortality.
Causes of foetal growth restriction?
The causes of fetal growth restriction can be divided into two categories:
1 - Placenta mediated growth restriction
2 - Non-placenta mediated growth restriction, where the baby is small due to a genetic or structural abnormality
Placenta mediated growth restriction refers to conditions that affect the transfer of nutrients across the placenta:
Idiopathic Pre-eclampsia Maternal smoking Maternal 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
What are other signs of FGR other than SGA?
There may be other signs that would indicate FGR other than the fetus being SGA, such as:
Reduced amniotic fluid volume
Abnormal Doppler studies
Reduced fetal movements
Abnormal CTGs
Complications of FGR?
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 SGA?
There are a long list of risk factors for SGA:
Previous SGA baby Obesity Smoking Diabetes Existing hypertension Pre-eclampsia Older mother (over 35 years) Multiple pregnancy Low pregnancy‑associated plasma protein‑A (PAPPA) Antepartum haemorrhage Antiphospholipid syndrome
How are women at risk of SGA monitored?
At the booking clinic, women are assessed for risk factors for SGA. Major + minor risk factors as per RCOG guidelines
Low-risk women have monitoring of the symphysis fundal height (SFH) at every antenatal appointment from 24 weeks onwards to identify potential SGA. 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 of SGA?
The critical management steps are:
Identifying 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
Karyotyping for chromosomal abnormalities
Testing for infections (e.g. toxoplasmosis, cytomegalovirus, syphilis and malaria)
Early delivery is considered when growth is static on the growth charts, or other problems are identified (e.g. abnormal Doppler results). This reduces the risk of stillbirth. Corticosteroids are given when delivery is planned early.
