The 18-20 Weeks Gestation Scan (Morphology Scan)

An ultrasound examination of your pregnancy is often recommended at 18-20 weeks gestation.

At this stage the sonographer or doctor can:

  • Confirm that the fetal heart is beating
  • Detect multiple pregnancies
  • Measure the fetal size
  • Assess the position of the placenta
  • Check the volume of amniotic fluid around the baby
  • Look for fetal abnormalities

Why scan the pregnancy at 18 weeks?

At 18-20 weeks gestation there are usually good views of the limbs as well as the internal organs. It is sometimes called an "anomaly scan" because fetal abnormalities are looked for at this time.

Why do I need a full bladder?

Fluid in the bladder provides a clear "window" to the pregnancy. It also makes the uterus rise up from behind your pubic bone. Your bladder does not need to be uncomfortably full, so feel free to empty some if you need to.

Can I find out the sex of the baby?

Ultrasound examination is never 100% accurate at determining the fetal sex. But if you want to know the sex, please let us know at the beginning of the examination so that we have several opportunities to view the region, and improve our accuracy for you.

What sorts of abnormalities can be detected?

Below is a list of different types of congenital abnormality, and how likely scanning is to identify each problem.

What if a problem is found?

If the scan finds a problem you will be told at the time of the scan that there is a problem, but a full discussion of the problem may require you to come back to the practice for a further scan and discussion with a specialist. Most problems that need repeat scanning are not serious and approximately 10% of scans will need to be repeated for one reason or another.

How safe is ultrasound?

Ultrasound uses sound waves, not ionizing radiation like x-rays. There have been many long term studies which have shown no adverse effect from an examination before birth. Follow-up has shown normal growth and development, normal eyesight and hearing and a normal range of school performance.