Anomaly scan

The anomaly scan is usually the second of two ultrasounds offered on the NHS during pregnancy. It takes place in the second trimester and is an opportunity for the sonographer to get a much more detailed picture of the baby’s health during crucial development phases.

When does the anomaly scan take place?

The scan is performed between 18 and 22 weeks depending on circumstances. It is worth noting that not all women choose to have the scan, but all will be offered it. You are supported throughout the decision-making process and given the information you need to make an informed choice.

How is the scan performed?

Women are regularly asked to drink something before the scan; this allows the bladder to become full and pushes the womb higher to give a better picture of the baby and uterus. Lying comfortably on your back, the sonographer applies jelly to the abdominal area and then runs a transducer over the area to send out and pick up sound waves. Pictures created by the scan are formed on a nearby screen. The process is painless, with mild discomfort at the most.

What is the primary purpose of the scan?

As the main pregnancy scan, an anomaly scan is used to take a precise look at the baby as its skeletal and organ formation continue. Through ultrasound imaging technology, the experienced sonographer is able to pinpoint multiple potential problems that can arise in developing foetuses. Although not all possible physical conditions can be picked up by the scan, a significant proportion of major irregularities can be found. These include spina bifida, cleft lip or palate, and abnormalities affecting the brain, heart or other organs. If fingers or toes are missing, these will also be caught by the scan.

For parents with a developing baby who is found to have one of these anomalies, identifying the problem this early is vital. It allows parents to adequately prepare before the birth, sometimes both emotionally and financially depending on the condition, and make any necessary arrangements or decisions.

What else does the sonographer look for?

As with all ultrasound scans, measurements are taken of the baby in order to assess foetal development, including organ and skeletal formation plus placental position and function. While the initial dating scan (see our article for more details) often gives only rudimentary data, focusing on the baby’s structure and growth at the stage of the anomaly scan is much more productive. This is because the baby has grown to the point that measurements such as the biparietal diameter, abdominal circumference, and femur length are all relevant. The abdominal circumference in particular is a crucial measurement in later pregnancy, as it clearly shows the baby’s growth and size, and can be used to diagnose growth retardation.

Girl or boy?

Traditionally this is also the scan where parents, if they choose, find out the sex of their baby. Remember that this is not the primary purpose of the scan, and also that ascertaining the baby’s sex may be more difficult than you think. For these reasons some hospitals do not tell any parents the sex; ask your hospital about their policy.

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