What is an anatomy scan?

An anatomy scan, also known as a mid-pregnancy ultrasound, takes a close look at your baby and your uterus. Your doctor will check that your baby is developing normally, and will look at where the placenta is lying. Although the anatomy scan is often called a 20-week scan you could have it any time between 18 weeks and 22 weeks.

What information will my anatomy scan provide?

• The shape and structure of your baby's head and brain. At this stage, severe brain problems, which happen very rarely, are visible.

• Your baby's face, to check for a cleft lip. Cleft palates inside a baby's mouth are hard to see and are not often picked up.

• Your baby's spine, both along its length, and in cross section, to make sure that all the bones align, and that the skin covers the spine at the back.

• Your baby's abdominal wall, to make sure it covers all the internal organs at the front.

• Your baby's heart. The top two chambers (atria) and the bottom two chambers (ventricles) should be equal in size. The valves should open and close with each heartbeat. Your sonographer will also examine the major veins and arteries which carry blood to and from your baby’s heart.

• Your baby's stomach. Your baby swallows some of the amniotic fluid that he lies in, which is seen in his stomach as a black bubble.

• Your baby's kidneys. The sonographer will check that your baby has two kidneys, and that urine flows freely into his bladder. If your baby's bladder is empty, it should fill up during the scan and be easy to see. Your baby has been peeing every half an hour or so for some months now!

• Your baby's arms, legs, hands and feet. The sonographer will look at your baby's fingers and toes.

• The placenta, umbilical cord and the amniotic fluid.

Source:
https://www.babycenter.ca/a557390/anatomy-scan-mid-pregnancy-ultrasound