Anatomy scan – fetal ultrasound – ultrasound screening for fetal anomalies

An anatomy scan (also known as fetal ultrasound, anomaly scan or anatomy ultrasound) is a test that checks the fetus’ development and detects fetal anatomy abnormalities and severe diseases. These are conditions that can affect the baby’s life and the parents’ wish to continue the pregnancy.

The scan is performed by a gynecologist (usually one specializing in gynecological ultrasonography). The test is performed using an ultrasound transducer for a detailed scan of all the fetus’ organs.


When is the scan performed?

There are several recommended stages for performing a fetal ultrasound. Generally, the earlier the scan is performed, the greater the chances of birth defects going undetected. However, these scans are usually performed early into pregnancy, especially if parents are considering terminating the pregnancy.

Considering the difficulty of setting a date for this scan, some prefer to perform two scans – one around week 17 and the other around week 22.

The test can be performed in a wide range of weeks into pregnancy. When abnormal results are detected, or when placental dysfunction is found, follow-up ultrasound scans are recommended in more advanced weeks of pregnancy.


Who should undergo the scan?

Fetal ultrasound scans are recommended to all pregnant women as part of routine prenatal testing. The scan is especially recommended to women with a higher risk for birth defects: a maternal age of 35 and over, women who suffered infections during pregnancy (particularly CMV), women with a family history of genetic disorders, and after irregular results in previous screening tests (nuchal translucency, triple scan, other ultrasound scans).


How is the scan performed?

The scan takes around an hour and does not involve any pain. Fetal ultrasounds are usually performed abdominally. the healthcare provider applies a gel to the abdomen and then moves the ultrasound transducer at different angles over the abdomen. This allows focusing on different parts of the fetus’ anatomy.

The test slowly examines important organs including the brain (including the ventricular system, cerebellum, and blood vessels), the heart (including chambers, valves and large blood vessels), the gastrointestinal tract (stomach, liver and intestines), the spleen, the urinary system, reproductive system (at this stage, it is possible to determine the fetus’ sex), limbs, face, spine, umbilical blood vessels, amniotic fluid, and more.

In addition to examining organs, doctors will also check several anatomical indexes to assess the fetus’ development: the circumference of the head, femur length, abdominal circumference, and biparietal diameter.

More advanced equipment can provide a three-dimensional image of the fetus. A 3-d ultrasound does not add to the efficiency of the anatomical assessment procedure but are nice to look at. Some healthcare providers allow parents to take a video or selected images from the scan, as a keepsake.


What diseases can the scan detect?

A fetal ultrasound scan can detect significant fetal anomalies in various organs. It is important to remember that the test is not meant to detect 100% of all birth defects. However, in skilled and attentive hands, the detection rate is rather high.

The scan can detect Down syndrome and other chromosome abnormalities such at Turner syndrome, infections affecting the fetus, and more. If a risk for a certain birth defect is detected, further tests are usually required. For instance, heart defects usually require a referral to a fetal cardiac scan preformed by a pediatric cardiologist. These tests can help add further important information.


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