The 20-week ultrasound, often called the anatomy or anomaly scan, is a significant milestone during pregnancy. This detailed examination is typically performed between 18 and 22 weeks of gestation, with the 20-week mark being the most common time. The primary purpose is to thoroughly evaluate the developing fetus, checking for structural growth and monitoring overall well-being. The scan provides a comprehensive look at the baby’s organs, limbs, and growth metrics. Additionally, it assesses the location of the placenta and the amount of amniotic fluid.
Preparing for the Anatomy Scan
Preparation for this appointment, which can take 45 minutes to an hour, focuses on practical steps to ensure the sonographer obtains clear images. Confirm the specific instructions regarding your bladder with the imaging center. At 20 weeks, a partially filled bladder may be recommended to help push the uterus higher for better imaging. Eating a light meal or snack before the scan may also be suggested, as the resulting fetal movement can sometimes help the technician capture all necessary views.
It is helpful to wear loose-fitting, comfortable clothing, ideally a two-piece outfit that allows easy exposure of your abdomen. This makes it simpler for the technician to apply the ultrasound gel and move the transducer across your skin. Gather necessary documentation beforehand, such as your healthcare provider’s referral form and reports from previous scans. Knowing your preference regarding the fetal sex beforehand is also useful, as the genitals are usually developed enough to be identified, though the baby’s position can sometimes obscure the view.
What the Sonographer Will Be Checking
The sonographer follows a systematic process, using a transducer and clear gel on your abdomen, to capture images and measurements of the fetus. This non-invasive examination utilizes sound waves to create detailed pictures of internal structures. A primary focus is placed on the fetal heart, where the technician confirms the presence of four chambers, assesses blood flow through the valves, and measures the heart rate.
Detailed attention is also given to the fetal brain, where the sonographer examines the skull shape, looks for symmetry, and checks key structures like the cerebellum and corpus callosum. They inspect the spine to ensure the vertebrae are properly aligned and the spinal cord is fully covered. Measurements of the head circumference, abdominal circumference, and long bones—like the femur and humerus—are taken to assess growth and estimate fetal weight.
The sonographer checks the major internal organs to confirm normal development and function. They look for the stomach bubble, which suggests the baby is swallowing amniotic fluid, and check the kidneys and bladder for fluid, confirming urine production. Furthermore, they examine the facial profile, specifically to look for conditions like a cleft lip. Beyond the fetus, the sonographer assesses the health and position of the placenta, specifically looking for placenta previa. They also check the umbilical cord for proper blood flow and the amount of amniotic fluid surrounding the baby.
Understanding the Findings and Follow-Up
In most cases, the anatomy scan provides reassurance, confirming that the fetus is developing appropriately and that major structures appear normal. The sonographer captures images and measurements, which are then reviewed by a radiologist or the referring healthcare provider. While the sonographer performs the technical scan, they typically do not share diagnostic interpretations; your provider will discuss the official results with you.
Follow-Up Scans
Sometimes, a follow-up scan is needed, often due to a non-concerning issue like fetal position making it difficult to visualize a specific organ. A re-check may also be required if the placenta is low-lying later in the pregnancy. In a small percentage of scans, minor findings, sometimes called soft markers, are identified that may require monitoring but often resolve on their own.
Significant Findings
If a finding is more significant, such as a suspected heart defect or an issue with a major organ, you may be referred to a maternal-fetal medicine specialist for further consultation or specialized testing like a fetal echocardiogram.
These follow-up steps are designed to gather more information and formulate an appropriate care plan, which could involve additional ultrasounds. Your healthcare team will use the detailed information from the 20-week scan to guide the remainder of your pregnancy and prepare for delivery.