The anatomy scan, also known as the level two ultrasound or anomaly scan, is a detailed, non-invasive procedure performed during the second trimester of pregnancy. This assessment uses sound waves to create images of the developing fetus, providing a comprehensive check of structural development and overall growth. It is a standard screening tool in prenatal care used to confirm that development is progressing as expected.
The Optimal Window for Scheduling
The fetal anatomy scan is typically scheduled between 18 and 22 weeks of gestation, with many providers aiming for the 20-week mark. This timing is chosen because the fetus is large enough for the sonographer to clearly visualize and measure all major organ systems.
The amount of amniotic fluid is also optimal during this window, which helps create clear ultrasound images. Scheduling the scan before 18 weeks may mean certain structures are not yet large enough to be properly assessed. Waiting much later than 22 weeks can make it harder to obtain clear images if the baby is positioned low in the pelvis.
Some providers schedule the scan closer to 18 weeks to allow time for a follow-up, while others prefer the greater detail available closer to 20 or 21 weeks. The specific timing depends on individual practice guidelines and the patient’s medical history.
What the Scan Examines in Detail
The anatomy scan is a comprehensive check of the baby’s entire body. This detailed assessment begins with biometry, which includes measuring the head circumference, abdominal circumference, and the length of the femur (thigh bone). These measurements estimate the baby’s weight and confirm that the growth rate is appropriate for the gestational age.
A significant portion of the scan focuses on examining the major organ systems. The sonographer checks the fetal brain, including structures like the ventricles and cerebellum, and the integrity of the skull. The heart is examined in detail, confirming the presence of four chambers and assessing blood flow to rule out congenital heart abnormalities.
The spine is viewed along its entire length to ensure the vertebrae are aligned and fully covered, checking for conditions like spina bifida. Other abdominal organs, including the stomach, kidneys, and bladder, are identified. The sonographer also assesses the limbs, notes the presence of hands and feet, and checks the location of the placenta and the volume of amniotic fluid.
Preparing for the Ultrasound Procedure
The anatomy scan generally takes longer than earlier ultrasounds, often lasting between 30 and 60 minutes, as the sonographer must capture numerous specific images. The procedure uses transabdominal ultrasound: a gel is applied to the abdomen, and a transducer wand is moved across the skin to generate real-time images.
Patients are sometimes advised to drink water beforehand to ensure a full bladder, which can help lift the uterus and provide clearer visualization. However, specific instructions vary between clinics, so confirm preparation requirements beforehand. Wearing loose-fitting clothing is also recommended for comfort.
During the scan, the sonographer focuses on acquiring high-quality diagnostic images for the interpreting physician. If the baby is not in an ideal position, the sonographer might ask the patient to shift positions or walk around briefly. This movement encourages the baby to move into a better viewing angle, allowing necessary images to be captured.
Understanding Follow-Up Scans and Results
It is common for the sonographer to be unable to get a clear view of every structure during the initial appointment, often due to the baby’s position or movement. If this happens, a repeat ultrasound, or follow-up scan, will be scheduled later to complete the examination. The need for a follow-up is usually not a cause for concern and is most often due to an “uncooperative” baby.
The results are reviewed by a radiologist or a maternal-fetal medicine specialist, and then communicated to the patient by their healthcare provider. If the findings are normal, the patient continues with routine prenatal care. In a small percentage of cases, the scan may indicate a soft marker or a potential structural anomaly requiring further investigation.
If an anomaly is suspected, the next step involves a referral to a specialist, such as a maternal-fetal medicine physician, for a more targeted ultrasound or diagnostic testing. This additional testing helps to confirm or rule out a diagnosis. Early detection allows the medical team to make informed decisions and prepare any necessary care plan for delivery and beyond.