The anomaly scan is one of the most important tests that you will have during pregnancy as it can provide vital information about your baby’s health and development. The scan is usually performed between 20 and 24 weeks and your baby will look very different if the last time you saw him or her was at the nuchal or dating scan.

Anomaly Scan


At 20 weeks, your baby should be about the size of a banana. During earlier scans, baby’s length was measured from crown to rump, but from now on the measurement will usually be given from the top of the head to the heel. Your baby should be about 10 inches long and will weight about 10.6 ounces. Other measurements such as the head size will also be taken during the 20 week anomaly scan to ensure that your baby is growing as expected.

How Your Baby is Developing

  • Babies are very active by 20 weeks so you will probably see some kicking, arm waving and stretching. You might even catch baby sucking a thumb.
  • Although you won’t be able to see it, babies are covered in a thick layer of fat at this stage in pregnancy. It is known as vernix caseosa and it helps to protect baby’s skin in the womb and as he or she passes along the birth canal.
  • It should be possible to tell whether your baby is a boy or girl at the 20 week ultrasound, although it might not be as obvious to you as it usually is to the sonographer.
  • Your baby will be able to hear what is going on outside the womb so he or she will be starting to learn to recognize familiar voices.

How Will Your Baby Look?

When you see your baby on the screen during your 20 week anomaly scan, you will notice a big difference from earlier scans. If it has been a while since your last ultrasound you may be surprised by how much easier it is to recognize your baby’s hands, feet and face. You should get a very clear look at his or her profile and your baby will look much more like a newborn.