The 20-week ultrasound, often called the anatomy scan or Level 2 ultrasound, is a major milestone in pregnancy care. This detailed imaging appointment uses sound waves to create a picture of the fetus and surrounding maternal structures. Scheduled halfway through the pregnancy, its primary focus is a systematic examination of the fetal body. This ensures all structures are forming as expected, providing reassurance for expectant parents.
The Purpose and Timing of the Anatomy Scan
This specialized ultrasound is performed between 18 and 22 weeks of gestation. During this period, the fetus is large enough for detailed assessment, and major organ systems are developed enough to be clearly visible and measurable.
The medical goals of the anatomy scan focus on growth metrics and structural integrity. One function is to accurately assess fetal development by taking specific measurements to verify gestational age and project estimated weight. The other goal is to screen for anatomical anomalies, which are structural differences that may require monitoring or intervention after birth.
Preparation and Logistics for the Appointment
A typical anatomy scan lasts between 30 and 60 minutes, varying based on the baby’s position and cooperation. The sonographer, the trained technician, captures all required images and measurements. You will lie on an examination table while the sonographer applies a clear, water-based gel to your abdomen. This gel helps the transducer glide smoothly and transmits the sound waves.
Some providers may request a full or partially filled bladder, especially earlier in the 18 to 20-week range, as the fluid improves the visibility of the uterus and cervix. The room lights are often dimmed to enhance the screen view. The sonographer may remain quiet during the exam to maintain concentration on capturing precise images. Many facilities permit one or two support people to join the session, but often limit attendees to minimize distractions.
The Detailed Fetal Anatomy Checklist
The sonographer systematically works through a comprehensive checklist, capturing images and measurements of the fetus from head to toe. Focusing on the head, the technician measures the Biparietal Diameter (BPD) and Head Circumference (HC). They examine the brain’s internal structures, such as the cerebellum and the fluid-filled ventricles, to confirm normal development and symmetry. Moving to the face, the sonographer checks the integrity of the lips and palate to screen for a cleft lip.
The heart is a major focus, requiring a four-chamber view to confirm the presence and proper formation of all four chambers and the great vessels. Measurements of the fetal heart rate, which typically falls between 120 and 180 beats per minute, are recorded. In the abdomen, the sonographer ensures the stomach bubble is visible, suggesting the baby is swallowing amniotic fluid, and checks for the presence of two kidneys and a bladder filled with urine, indicating proper kidney function.
The entire length of the spine is examined in both longitudinal and cross-sectional views to confirm the vertebrae are aligned and that the spinal cord is fully covered by skin. For the extremities, the sonographer measures the length of bones like the femur (Femur Length or FL) and humerus to assess growth. They confirm the presence of all four limbs, hands, and feet. The sonographer will attempt to count fingers and toes if the fetal position allows for a clear view.
The assessment extends to the support systems sustaining the pregnancy. The location of the placenta is noted to check for conditions like placenta previa, where the placenta covers the cervix. The umbilical cord is examined to confirm it contains the expected three vessels—two arteries and one vein. The volume of amniotic fluid surrounding the fetus is measured to ensure the levels are within a normal range.
Interpreting the Visuals and Findings
The images you see during the scan are primarily two-dimensional (2D), displaying cross-sectional slices in shades of gray to highlight different tissues. These 2D images are the standard for medical assessment because they provide the necessary contrast for measuring internal structures and organs. Some clinics may offer brief glimpses using three-dimensional (3D) or four-dimensional (4D) ultrasound, which creates a surface view of the baby’s features.
The image clarity at 20 weeks allows parents to make out features like the profile, hands, and feet. If requested, the sonographer can usually determine the baby’s sex, provided the external genitalia are clearly visible and the baby is positioned favorably.
After the scan, the sonographer communicates whether the initial findings appear “normal,” meaning all checklist structures were visualized and measured correctly. If a structure is temporarily obscured by the baby’s position, a repeat scan may be recommended later. If the sonographer identifies a potential anomaly, they alert your healthcare provider, who will discuss the findings and arrange a consultation with a specialist for further testing.