What Is the Difference Between a Detailed Anomaly Scan and a 4D Ultrasound?
Jun 20, 2022
Source: Cainiu Health
Dr. Wang Huiying
Introduction
Four-dimensional (4D) ultrasound and the “major anomaly scan” are two distinct examinations, differing in both content and timing. The major anomaly scan is typically performed between weeks 20 and 24 of pregnancy. In contrast, 4D ultrasound can be conducted between weeks 20 and 40 of gestation. During the 4D ultrasound examination, the fetal eye sockets and both eyes are assessed, and measurements—including interocular distance and lip morphology—are taken.
The “Four-Dimensional Ultrasound” (4D ultrasound) and the “Detailed Anomaly Scan” are two distinct prenatal examinations, differing in both timing and scope.
1. Timing Differences: The Detailed Anomaly Scan is a comprehensive B-mode ultrasound examination primarily aimed at detecting structural abnormalities in fetal development, thereby enabling early identification and exclusion of major congenital anomalies. This scan is typically performed between weeks 20 and 24 of gestation. In contrast, the 4D ultrasound can be performed between weeks 20 and 40 of pregnancy, as by this time the fetus’s limbs and major organs have fully developed, allowing clear visualization of fetal anatomy and growth via ultrasound.
2. Scope Differences: During the 4D ultrasound, specific assessments include evaluation of the fetal orbits and both eyes, measurement of interocular and biparietal distances, and examination of the fetal neck for any abnormal masses or swelling. Conversely, the Detailed Anomaly Scan focuses on a systematic assessment of fetal organs and external body structures to evaluate overall fetal health and detect potential structural abnormalities.
Note: Some hospitals may not offer 4D ultrasound capabilities and instead perform anomaly screening using 3D or 2D ultrasound. As a result, certain patients may perceive these examinations as identical—or even equate the 4D ultrasound with the Detailed Anomaly Scan—though they remain conceptually and technically distinct procedures.
