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The use of ultrasound has revolutionised obstetric management over the past three decades, as it allows direct visualisation of the foetus, the placenta and the uterus. It is used specifically to: - establish viability in very early pregnancy
- establish foetal age
- determine placental and foetal position
- diagnose multiple pregnancy
- assess foetal anatomy and the presence of any congenital abnormality.
- monitor foetal growth in later pregnancy
- guide amniocentesis for the exclusion of chromosomal abnormality.
Obstetric scans should only be performed where there is a specific indication. The most commonly requested first scan is at 10 – 14 weeks where age is accurately established and the nuchal translucency (depth of fluid below the skin of the neck) is measured. This helps to give an assessment of the risk of chromosomal abnormality. The second routine scan at 20 – 24 weeks gives an excellent detailed picture of foetal anatomy. Further scans are usually requested only when there is a clinical indication on antenatal examination.
Doppler ultrasound can be used to show heart activity as well as umbilical and placental blood flow. It is particularly useful in monitoring foetal condition where there is growth retardation in later pregnancy.
Preparation for an Obstetric Ultrasound
No specific preparation is needed.
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