Is “Si Wei” (Four-Dimensional Ultrasound) the same as the major fetal anomaly scan?

Four-dimensional (4D) color Doppler ultrasound is currently one of the most important prenatal examinations. Its primary purpose is to screen for congenital fetal anomalies. While the objectives of 4D ultrasound and the “major anomaly scan” (also known as the “anatomy scan” or “level II ultrasound”) are essentially identical, the latter encompasses additional assessments—such as nuchal translucency (NT) measurement and Down syndrome screening.

Is 4D Ultrasound the Same as the Major Anomaly Scan?

Although there are subtle distinctions between 4D ultrasound and the major anomaly scan, their clinical purposes largely overlap. Specifically, the major anomaly scan includes 4D ultrasound as one of its core components, along with NT measurement and Down syndrome screening. NT measurement primarily evaluates early fetal brain development, while Down syndrome screening aims to identify the risk of trisomy 21 (Down syndrome), which is associated with intellectual disability. As 4D ultrasound constitutes the final component of the major anomaly scan, it is often regarded—clinically—as synonymous with the major anomaly scan itself.

During a 4D ultrasound examination, clinicians assess whether the fetus exhibits facial abnormalities such as cleft lip or cleft palate; structural brain anomalies including hydrocephalus, microcephaly, spina bifida, meningocele, or anencephaly; and malformations affecting the digestive system, urinary system, and limbs. Therefore, whether undergoing the comprehensive major anomaly scan or standalone 4D ultrasound, both examinations are highly recommended during pregnancy.

Additionally, pregnant women should be aware of optimal timing for various screenings: NT measurement is typically performed around gestational week 12; Down syndrome screening (e.g., serum marker testing or combined first-trimester screening) is usually conducted around week 16; and 4D ultrasound is ideally scheduled between weeks 24 and 28. Adhering to these recommended timeframes ensures maximum diagnostic accuracy; delays may compromise detection sensitivity. If uncertain about scheduling, expectant mothers should consult their local obstetrician or maternal-fetal medicine specialist, who can tailor the examination schedule according to individual fetal development. Furthermore, maintaining a healthy lifestyle—including balanced nutrition, adequate rest, and avoidance of harmful substances—is strongly advised to support optimal fetal health.

The above provides an overview of whether 4D ultrasound equates to the major anomaly scan. We hope this information proves helpful.