What will be examined at the 20 week scan?

What is examined at the 20 week scan?

Your baby's internal organs are examined in cross sectional views, or "slices" of your baby, which may be difficult — if not impossible — for you to make out! Bones will look white on the scan, fluid will be black and soft tissues will look grey and speckled.

The head
The head is usually examined first. A normal head is rugby-ball shaped with a mid-line separating the two halves of the brain which are surrounded by fluid. There is a dumb-bell shaped structure called the cerebellum (hindbrain) at the back of the head.

Spine and abdominal wall
The sonographer will check your baby's spine in both the long view and in cross section, moving through the neck and shoulders to the pelvis. She is making sure that all the vertebrae are in alignment, that the skin covers the spine at the back and the baby's abdominal wall covers all the internal organs at the front.

Heart and stomach
She will look at the heart, which should occupy a third of the chest and point to the left. The top two chambers, or "atria", and the bottom two chambers, or "ventricles", should be equal in size and the valves should open and close with each heartbeat. She will then look beneath the diaphragm to see the stomach, under the heart on the left side. Your baby swallows some of the amniotic fluid that it lies in; this can be seen in the stomach as a black bubble.

Kidneys and bladder
The two kidneys are either side of the spine, below the stomach and are usually quite hard to see. If the bladder is full, it's easy to see as a black bubble in the pelvis. If it is empty it should fill up during the scan — your baby has been weeing every half an hour or so for some months now!
Hands and feet
The long bones and position of hands and feet are examined; the fingers and toes are looked at but not counted.

Placenta, umbilical cord and amniotic fluid
The placenta may be on the front or the back wall of your womb, usually near the top (or fundus) so may be described as "fundal" on your scan report. Many are described as "low" because they reach down to or cover the neck of the womb (cervix). If your placenta is low, another scan will be arranged in the third trimester, by which time most placenta will have moved away from the cervix. (Read more about having a low-lying placenta.)
It is possible to count the three vessels in the umbilical cord but this may not be done routinely. There should be enough amniotic fluid surrounding the baby to allow it to move freely at this stage.