What is the difference between Down syndrome screening and four-dimensional ultrasound?

Jul 19, 2025 Source: Cainiu Health

Dr. Zhang Lu

Introduction

Down syndrome screening, or Down syndrome test, and four-dimensional ultrasound (4D ultrasound) differ in several aspects, including examination purpose, method, timing, content, and the significance of results. When undergoing Down syndrome screening and 4D ultrasound, it is important to follow the schedule recommended by the physician. If abnormal results are found, further examinations should be conducted under the guidance of a doctor.

Down's screening refers to Down syndrome screening, while four-dimensional refers to four-dimensional color ultrasound. Under normal circumstances, there are differences between Down syndrome screening and four-dimensional color ultrasound in terms of examination purposes, methods, timing, content, and the significance of results. Detailed analysis is as follows:

1. Examination Purpose: Down syndrome screening primarily aims to detect whether the fetus suffers from chromosomal abnormalities such as Down syndrome and assess the risk of disease; four-dimensional color ultrasound mainly observes whether there are structural malformations in the fetus, such as the development of the face, limbs, and internal organs.

2. Examination Method: Down syndrome screening involves drawing the pregnant woman's blood to test related indicators in the blood, then calculating the risk value in combination with factors such as the woman's age. Four-dimensional color ultrasound uses ultrasound technology to scan the pregnant woman's abdomen with a probe and displays real-time dynamic images of the fetus.

3. Examination Timing: Down syndrome screening is generally performed between 15 to 20 weeks of pregnancy, when related blood indicators are relatively stable, thereby improving screening accuracy; four-dimensional color ultrasound is usually conducted between 22 to 26 weeks of pregnancy, when the fetus's organs have largely developed completely, making structural observation clearer.

4. Examination Content: Down syndrome screening focuses on chromosomal number abnormalities, especially trisomy 21 and trisomy 18; four-dimensional color ultrasound focuses on checking the fetus's physical structure, including whether there are morphological abnormalities in the skull, spine, heart, kidneys, etc.

5. Significance of Results: The result of Down syndrome screening is a risk value indicating the likelihood of the fetus having a disease, but it does not provide a definitive diagnosis; the result of four-dimensional color ultrasound directly shows whether there are structural abnormalities in the fetus, providing visual evidence for diagnosing structural malformations.

When undergoing Down syndrome screening and four-dimensional color ultrasound, it is important to follow the doctor's recommended schedule for timely examinations. If abnormal results occur, further examinations or appropriate actions should be taken following the doctor's instructions to ensure pregnancy safety.

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Can I choose between a major anomaly scan and a four-dimensional ultrasound?

Under normal circumstances, pregnant women can choose between a detailed anomaly scan (Big Anomaly Scan) and a four-dimensional ultrasound (4D ultrasound). Both the Big Anomaly Scan and 4D ultrasound are important prenatal examinations used to assess fetal health. They have overlapping aspects in terms of examination content and purpose, and both offer high accuracy. Therefore, pregnant women can choose one of these examinations during their pregnancy. It is also important for pregnant women to maintain a positive and optimistic mindset in daily life and undergo regular prenatal checkups.

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What should I do if I keep failing the four-dimensional ultrasound?

The inability to obtain clear four-dimensional ultrasound images can often be improved by adjusting the examination timing, engaging in moderate activity, replenishing energy, relaxing mentally, or changing body positions during the scan. In most cases, this issue is related to unfavorable fetal positioning and does not require excessive anxiety. However, if multiple attempts still fail to produce adequate images, or if other abnormal indicators are present, it is recommended to seek timely medical advice from a professional doctor.

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What should I do if a butterfly vertebra is detected during a four-dimensional ultrasound?

Butterfly vertebra is a relatively rare spinal developmental anomaly, typically referring to incomplete fusion of the middle portion of the vertebral body, resulting in a shape resembling butterfly wings. When a butterfly vertebra is detected during a four-dimensional examination, timely specialist consultation is required, along with further diagnostic tests, assessment of spinal development, formulation of an individualized intervention plan, and regular follow-up monitoring. If associated with other severe malformations, additional evaluation is necessary.

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Is it necessary to have an echocardiogram if the four-dimensional ultrasound shows no abnormalities?

Even if the 4D ultrasound shows no abnormalities, it is still recommended to undergo a fetal echocardiogram according to standard prenatal guidelines. The two examinations focus on different aspects: 4D ultrasound emphasizes overall fetal structural screening, while fetal echocardiography focuses on detailed cardiac anatomy and functional assessment, enabling the detection of heart problems that may be missed by 4D ultrasound. If there are high-risk factors or abnormal findings during pregnancy, timely medical consultation and further evaluation are advised.