The anatomy scan, often called the 20-week ultrasound, is a detailed, non-invasive imaging procedure performed typically between 18 and 22 weeks of pregnancy. This mid-point check uses high-frequency sound waves to create images of the developing fetus and surrounding maternal structures. The main goal of this examination is to assess fetal growth and the development of major organs and body systems. The scan also provides information about the placenta’s position and the volume of amniotic fluid.
The Patient Experience: Preparation and Procedure
The anatomy scan appointment often lasts longer than earlier ultrasounds, typically taking between 30 and 60 minutes to complete. Preparation may involve drinking fluids beforehand to ensure a full or partially full bladder. A full bladder acts as an acoustic window, pushing the uterus higher and moving bowel gas away, allowing for better imaging of lower structures.
Upon entering the examination room, which is often dimly lit to improve screen visibility, you will be asked to lie down on an examination table. A clear, warmed gel is applied to your abdomen. The sonographer then moves this handheld device across your belly, applying gentle but sometimes firm pressure to obtain the necessary views.
During the procedure, the sonographer systematically works through a comprehensive checklist, freezing the screen and making numerous measurements and image captures. They may ask you to shift your position, cough, or briefly walk around if the fetus is positioned awkwardly, as a clear view of every structure is required for a complete study.
Structures and Measurements Evaluated
The sonographer begins by taking a series of standardized biometrics to confirm appropriate growth for the gestational age. These include the head circumference (HC), abdominal circumference (AC), and the length of the femur (FL), which are compared against established growth charts.
A significant portion of the scan focuses on internal anatomy, starting with the brain where the sonographer checks the shape of the skull, the symmetry of the hemispheres, and the presence of key landmarks like the cerebellum and ventricles. The four chambers of the heart are meticulously assessed, along with the correct outflow of the major blood vessels, which is a detailed check known as a limited fetal echocardiogram.
The spine is examined from the neck down, ensuring all vertebrae are aligned and covered by skin. The sonographer also assesses external structures, checking the face for a complete lip and palate, and confirming the presence of all digits and normal movement in the limbs, hands, and feet. Other abdominal organs checked include:
- The stomach, which should contain fluid to confirm the fetus is swallowing amniotic fluid.
- The kidneys and bladder, confirming the production and excretion of urine.
The surrounding support structures are also documented. The sonographer determines the location of the placenta, noting its position relative to the cervix, and checks the umbilical cord for the correct number of blood vessels, typically two arteries and one vein. Finally, the volume of amniotic fluid is measured, as too much or too little fluid can indicate underlying issues. If the fetus is in a favorable position, the sonographer can also determine the fetal sex.
Understanding the Findings
After the sonographer completes the technical imaging process, the collected images and measurements are compiled into a comprehensive report. The sonographer acquires the necessary data, but they generally do not provide a medical diagnosis or interpret the findings for the patient. The official results and diagnosis come from a qualified physician, such as a radiologist or a maternal-fetal medicine specialist, who reviews the images.
The timeline for receiving official feedback can vary depending on the facility. In many practices, the philosophy of “no news is good news” applies, meaning you will be contacted quickly if a finding requires immediate attention. If everything appears routine, the results are simply added to your medical chart.
Sometimes, the initial scan may be considered incomplete, often due to the fetus’s position, which prevents a clear view of a specific structure like the spine or heart. This is a common occurrence, and it simply requires a follow-up visit, known as a repeat or limited scan, to capture the missing images. If a potentially concerning finding, sometimes called a soft marker, is noted, a more detailed Level II ultrasound or a consultation with a specialist may be recommended.