Small / Large for Gestational Age Flashcards
What is meant by small for gestational age (SGA)?
when a fetus measures below the 10th centile for their gestational age
What ultrasound measurements are used to assess fetal size?
- estimated fetal weight (EFW)
- fetal abdominal circumference (AC)
(abdominal circumference is always measured at the level of T12)
What ultrasound measurements can be used to calculate EFW?
- biparietal diameter (BPD)
- head circumference (HC)
- abdominal circumference (AC)
- femur length (FL)
What is used to assess the size of the fetus?
customised growth charts
- these are based on the mother’s weight, height, parity + ethnic group
What is severe SGA?
when the fetus is below the third centile for their gestational age
What is a low birth weight?
birth weight of less than 2500g
How is fetal growth monitored on a customised growth chart?
- both symphysis-fundal height** and **estimated weight by scan are plotted on the chart
- growth can be compared to the decile lines
- and any plateau in growth can be detected
What are the 2 categories of causes of SGA?
constitutionally small:
- the fetus is small in size but matches the mother / others in the family
- it is growing appropriately on the growth chart
fetal growth restriction (IUGR):
- there is a small fetus or one that is not growing as expected
- this is due to pathology reducing the delivery of oxygen / nutrients to the fetus through the placenta
What are the 2 categories of causes of intrauterine growth restriction?
(IUGR = FGR)
- placenta mediated growth restriction
-
non-placenta mediated growth restriction
- small due to genetic / structural abnormality
What causes placenta mediated growth restriction?
conditions that affect the transfer of nutrients across the placenta:
- pre-eclampsia
- maternal smoking / alcohol
- anaemia
- malnutrition
- infection
- maternal health conditions
- idiopathic
What causes non-placenta mediated growth restriction?
pathology of the fetus, such as:
- genetic abnormalities
- structural abnormalities
- fetal infection
- errors of metabolism
Other than SGR, what other factors can suggest IUGR?
- reduced amniotic fluid volume
- abnormal doppler studies
- reduced fetal movements
- abnormal CTGs
What are the short-term complications of IUGR?
- fetal death / stillbirth
- birth asphyxia
- neonatal hypothermia
- neonatal hypoglycaemia
What are the long-term implications for growth-restricted babies?
- cardiovascular disease (particularly hypertension)
- diabetes
- obesity
- mood / behavioural problems
What are the modifiable risk factors for SGA?
- obesity
- smoking
- diabetes
- existing hypertension
What are the non-modifiable risk factors for SGA?
- previous SGA baby
- pre-eclampsia
- older mother (over 35)
- multiple pregnancy
- low PAPP-A
- antepartum haemorrhage
- antiphospholipid syndrome
How are low-risk women monitored for SGA?
monitoring the symphysis-fundal height (SFH):
- this is performed at every antenatal appointment from 24 weeks
- SFH is plotted on a customised growth chart
What is done in low-risk women if SFH is below the 10th centile?
women are booked for serial growth scans with umbilical artery doppler
What is done in low-risk women if SFH is below the 10th centile?
women are booked for serial growth scans with umbilical artery doppler
When are women booked for serial growth scans with umbilical artery doppler?
- 3** or more **minor risk factors
- 1** or more **major risk factors
- issues with measuring the SFH
- e.g. large fibroids / BMI > 35
What is measured on serial USS scans for women with SGA or at risk of SGA?
- estimated fetal weight (EFW)** and **abdominal circumference (AC) to determine growth velocity
- umbilical arterial pulsatility index (UA-PI) to measure flow through the umbilical artery
- amniotic fluid volume
these tend to be performed every 4 weeks from 28 weeks gestation
What are the critical management steps for SGA?
- identify those at risk of SGA
- aspirin** to anyone at risk of **pre-eclampsia
- treat modifiable RFs (e.g. smoking)
- serial growth scans to monitor growth
- early delivery where growth is static (or other concerns)
What investigations are performed to identify the underlying cause of SGA?
- blood pressure + urine dip for pre-eclampsia
- uterine artery doppler scanning
- detailed fetal anatomy scan by fetal medicine
- karyotyping for chromosomal abnormalities
- testing for infections
- syphilis
- malaria
- toxoplasmosis
- cytomegalovirus
When is early delivery considered and why?
- when growth is static on growth charts
- OR there are other problems (e.g. abnormal Dopplers)
- early delivery reduces the risk of stillbirth
What is meant by large for gestational age (macrosomia)?
- an estimated fetal weight above the 90th centile
- newborn weight > 4.5kg
What are the causes of macrosomia?
- constitutional
- maternal diabetes
- previous macrosomia
- maternal obesity / rapid weight gain
- overdue
- male baby
What are the risks to the mother associated with macrosomia?
- shoulder dystocia
- failure to progress
- perineal tears
- instrumental delivery / C-section
- postpartum haemorrhage
- uterine rupture (rare)
What are the risks to the fetus associated with macrosomia?
- birth injury
- e.g. Erbs palsy
- clavicular fracture
- fetal distress / hypoxia
- neonatal hypoglycaemia
- obesity in childhood / later life
- T2DM in adulthood
What are the investigations for a large for gestational age fetus?
- USS to exclude polyhydramnios + estimate the fetal weight
- oral glucose tolerance test for gestational diabetes
What is the advice about delivery of a macrosomic fetus?
- most women with a large for gestational age fetus will have a successful vaginal delivery
- induction of labour** is **AVOIDED in macrosomia
What is the main risk associated with macrosomia during delivery?
shoulder dystocia
How is the risk of shoulder dystocia diminished during delivery?
- delivery on a consultant led unit with experienced midwife / consultant
- access to a theatre if required
- early decision for C-section if required
- active management of the third stage
