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Are both the detailed anomaly scan and 4D ultrasound necessary?

Jan 04, 2022 Source: Cainiu Health
Dr. Yu Jiang
Introduction
Do I need both the detailed anomaly scan and 4D ultrasound? You do not necessarily need to undergo both the detailed anomaly scan and 4D ultrasound. The “detailed anomaly scan” refers specifically to a color Doppler ultrasound examination for fetal structural anomalies. Typically, pregnant women undergo this detailed anomaly scan between 18 and 24 weeks of gestation. Its primary purposes are to: assess whether fetal development in utero is consistent with gestational age; evaluate overall fetal health; detect structural abnormalities in the limbs, brain, and internal organs; and examine amniotic fluid volume and umbilical cord status.

Both the comprehensive fetal anomaly scan (“major anomaly screening”) and 4D ultrasound are important prenatal examinations, enabling assessment of fetal development, overall health status, and identification of various potential risks. However, some pregnant women find that the purposes and functions of these two examinations appear highly similar—leading to uncertainty about whether both are truly necessary, and concerns that undergoing both may be redundant. Below, we explore this question in detail.

Are Both the Comprehensive Anomaly Scan and 4D Ultrasound Necessary?

It is not mandatory to undergo both the comprehensive anomaly scan and 4D ultrasound. The “comprehensive anomaly scan” refers specifically to a detailed color Doppler ultrasound examination for fetal structural anomalies. Typically performed between 18–24 weeks of gestation, this scan primarily evaluates whether fetal development aligns with gestational age; assesses overall fetal health; examines for structural abnormalities in limbs, brain, and internal organs; and evaluates amniotic fluid volume and umbilical cord status. Pregnant women should schedule this ultrasound according to their healthcare provider’s recommended timing. Currently, three modalities are available: 2D, 3D, or 4D ultrasound.

4D ultrasound provides dynamic, real-time imaging of the fetal face and organ development, aiding in the detection and screening of congenital structural anomalies. It offers accurate, scientific evidence for early diagnosis of fetal surface malformations (e.g., cleft lip/palate) and complex congenital anomalies. Additionally, it can clearly visualize conditions such as fetal multicystic dysplastic kidney and renal hypoplasia, and holds significant value in diagnosing congenital heart disease.

Scope of the comprehensive anomaly scan: This examination systematically evaluates gross anatomical structures of the fetus—including both external features and internal organs. Prenatally diagnosable anomalies include severe cranial abnormalities (e.g., anencephaly, severe hydrocephalus, hydranencephaly, severe encephalocele, alobar holoprosencephaly), severe cystic hygroma, single ventricle, severe thoracoabdominal wall defects with evisceration, severe omphalocele, teratomas >5 cm in diameter, lethal achondroplasia, severe open spina bifida, and severe deficiencies of long bones including the femur, tibia, fibula, humerus, pubis, and radius.

The above overview outlines key considerations and distinct clinical utilities of the comprehensive anomaly scan and 4D ultrasound. If a pregnant woman wishes to pursue either or both examinations, she should first familiarize herself with the different modalities and relevant precautions. In most cases, performing both tests is unnecessary. Provided the fetal health status is adequately assessed and no significant concerns are identified, there is generally no clinical justification for conducting both examinations concurrently.

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What dimension of ultrasound is the "major anomaly scan"?
In general, the detailed anomaly scan can be performed using two-dimensional, three-dimensional, or four-dimensional ultrasound. The full name of this scan is "mid-trimester fetal ultrasound screening for major anomalies," which refers to an ultrasound examination conducted during the middle stage of pregnancy. The optimal time for mid-trimester anomaly screening is between 18 and 24 weeks of gestation, as this period is best suited for evaluating fetal anatomy and detecting structural abnormalities.
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Dr. Lv Aiming
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Is the major anomaly scan classified as level two or level three?
Major anomaly screening generally falls under Level 3 prenatal screening. It primarily refers to a four-dimensional color ultrasound examination performed between 22 and 28 weeks of pregnancy to determine whether fetal abnormalities are present. This examination allows for a clear assessment of whether the fetus's limbs, body, and internal organs show any abnormalities. During the 4D ultrasound, the movements of the fetus within the uterine cavity can be directly observed on an electronic screen.
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Dr. Lv Aiming
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Can a detailed anomaly scan detect toxoplasmosis infection?
In general, major anomaly screening cannot detect toxoplasmosis infection. Major anomaly screening refers to a series of examinations and screening methods used to comprehensively evaluate the physical condition and structural development of the fetus, in order to identify potential congenital abnormalities and malformations. These examinations include ultrasound scans, blood tests, and other imaging studies, aiming to detect and assess fetal developmental abnormalities as early as possible.
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Dr. Lv Aiming
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Does the major anomaly scan include an examination of the reproductive system?
Anomaly scan is a routine prenatal screening examination primarily used to assess fetal development and rule out potential congenital abnormalities. The anomaly scan is usually performed between the 18th and 20th weeks of pregnancy, using ultrasound imaging to observe the fetus's organs and structures. During the anomaly scan, the doctor thoroughly examines various fetal organs and systems, including the reproductive system.
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Dr. Lv Aiming
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Which is better: 4D ultrasound or major anomaly scan?
4D ultrasound and anomaly scan (detailed structural scan) each have their strengths in fetal examination: 4D ultrasound is better for assessing the fetal heart, while the anomaly scan is superior for detecting overall fetal developmental abnormalities. 4D ultrasound is primarily used to check for congenital heart defects, aiding in the diagnosis of conditions such as fetal rheumatic heart disease and tetralogy of Fallot. It provides a clearer, three-dimensional visualization of the fetal heart's thickness, shape, and size.
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Can a 4D ultrasound be performed at five months?
Can a 4D ultrasound be performed at five months? Yes, a 4D ultrasound can be performed at five months of pregnancy. In fact, 4D ultrasounds can be conducted at various stages of pregnancy; however, the visibility of fetal structures varies depending on the fetus’s size and developmental stage. Nevertheless, it is generally recommended to schedule the 4D ultrasound after five months of gestation. This is because certain fetal organ systems may not yet be fully developed earlier in pregnancy, further supporting the recommendation to perform the 4D ultrasound after five months.
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What should I do if I’ve had more than ten 4D ultrasounds without success?
Undergoing multiple 4D ultrasounds during pregnancy without obtaining satisfactory results warrants investigation into the underlying cause. If the unsatisfactory results are due to fetal malformations, further diagnostic evaluations—such as detailed ultrasound examination or amniocentesis—should be performed to assess for structural abnormalities; in severe cases, termination of pregnancy may be necessary. Alternatively, if suboptimal imaging is attributable to maternal obesity or unfavorable fetal positioning, the mother should reposition herself and undergo repeat imaging at a qualified hospital.
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Is “Si Wei” (Four-Dimensional Ultrasound) the same as the major fetal anomaly scan?
Is “4D ultrasound” the same as the “major anomaly scan”? There is a certain distinction between 4D color Doppler ultrasound and the major anomaly scan; however, their purposes are essentially the same. The major anomaly scan encompasses 4D color Doppler ultrasound, as well as nuchal translucency (NT) measurement and Down syndrome screening. NT measurement primarily assesses fetal brain development.
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Dr. Duan Xiaohua
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