The anatomy scan, also known as the level 2 ultrasound or the 20-week scan, is a standard, detailed examination performed during the second trimester of pregnancy. This non-invasive imaging procedure typically takes place between the 18th and 22nd weeks of gestation. Its primary function is to provide a comprehensive assessment of the developing fetus, ensuring growth is on track and checking for structural anomalies in the fetal anatomy. This examination offers detailed insights into the well-being of the pregnancy.
Expected Duration and Timing Variables
The anatomy scan appointment generally takes a minimum of 30 minutes, frequently extending to 45 or even 60 minutes. This duration reflects the extensive checklist the sonographer must follow to thoroughly document all required fetal structures. The sonographer systematically captures numerous specific images and measurements. This process cannot be rushed without risking incomplete data.
Several factors can influence how long the scan takes, most notably the position of the fetus. If the baby is positioned awkwardly, such as facing the mother’s spine or curled up, obtaining clear views of the heart, spine, or face may be difficult. In these situations, the sonographer may ask the patient to take a short break, walk around, or gently shift position to encourage the fetus to move. Maternal body habitus, sometimes referred to as BMI, can also affect the clarity of the ultrasound images, potentially requiring more time to acquire adequate visual data.
Preparing for the Anatomy Scan Appointment
Before the anatomy scan, patients should confirm the specific instructions regarding bladder preparation, as requirements can vary between clinics. For mid-trimester scans, some facilities may request a full bladder to help lift the uterus and improve the visibility of the lower uterine segment and cervix. This usually involves drinking a specified amount of water about an hour before the appointment and avoiding urination.
Patients should wear comfortable, loose-fitting clothing that allows the abdomen to be easily exposed for the application of the ultrasound gel and the transducer. Arriving on time is necessary, as late arrivals may need to be rescheduled to ensure the sonographer has adequate time for the detailed examination. Some providers suggest eating a small meal before the appointment. The resulting increase in maternal blood sugar may stimulate fetal movement, which can sometimes aid in capturing necessary images.
Key Fetal Measurements and Assessments
The core of the anatomy scan involves a systematic structural survey and fetal biometry, which is the process of measuring the baby’s size. Biometric measurements are taken to estimate fetal weight and confirm that growth aligns with the gestational age. These include the Head Circumference (HC), the Biparietal Diameter (BPD)—a measurement across the head—the Abdominal Circumference (AC), and the Femur Length (FL).
The structural assessment focuses on a detailed examination of every major organ system. The sonographer carefully inspects the fetal brain, checking for symmetry and the presence of specific structures like the cerebellum and the cavum septi pellucidi. The heart is examined in a four-chamber view, and the flow of blood through the major vessels, known as the outflow tracts, is observed.
Beyond the head and heart, the spine is viewed in both longitudinal and transverse planes to ensure the vertebrae are properly aligned and the skin covers the spinal cord. The sonographer will also check the kidneys, bladder, and stomach to confirm they are present and functioning correctly. The number of vessels in the umbilical cord is counted, the location of the placenta is mapped, and the volume of amniotic fluid surrounding the fetus is measured to complete the comprehensive assessment.