How 3D and 4D Ultrasound Work: Images, Motion and What Parents See

3D ultrasound creates a three-dimensional volume or rendered image. 4D ultrasound displays sequential 3D volumes over time. Learn what each does and what they do not replace.

3D ultrasound acquires a volume of ultrasound data that can be displayed in multiple planes or rendered as a three-dimensional surface. 4D ultrasound adds time: it repeatedly acquires and displays 3D volumes, creating a moving three-dimensional view. In simple terms, 3D is volume; 4D is volume changing over time. [13, 15, 16]

Educational visual of how 3D volume imaging and 4D motion relate. Educational illustration; not a diagnostic ultrasound image.
Visual overview of 3D images, 4D motion, and what parents typically see. Educational illustration; not a diagnostic ultrasound image.

3D ultrasound creates a three-dimensional volume or rendered image. 4D ultrasound displays sequential 3D volumes over time. Learn what each does and what they do not replace.

Educational schematic of 2D, 3D, and 4D ultrasound concepts. Educational illustration; not a diagnostic ultrasound image.
3D is a volume; 4D is that volume repeated over time. Neither is a camera photograph. Educational illustration; not a diagnostic ultrasound image.

How 3D ultrasound works

Conventional 2D ultrasound produces real-time cross-sectional images. In 3D ultrasound, multiple adjacent image planes are acquired into a volume dataset. The dataset can then be reviewed in orthogonal planes, rotated or rendered to display surfaces. This is useful because the examiner can explore spatial relationships after acquisition. [11, 12, 13, 14]

Educational pipeline diagram titled why a rendered 3D ultrasound can look different from a photograph, from ultrasound echoes through 2D frames, volume acquisition and surface rendering to a displayed 3D face. Educational illustration; not a diagnostic ultrasound image.
Why a rendered 3D ultrasound can look different from a photograph: echoes become 2D frames, then a volume, then a displayed surface. Educational illustration; not a diagnostic ultrasound image.

How 4D ultrasound works

4D imaging repeats 3D volume acquisition rapidly enough to display motion. This can show changing facial surfaces and fetal movements. Research has used 4D ultrasound to study fetal facial movements such as mouthing and yawning. [16]

Is 4D more accurate than 3D?

Not as a general rule. '4D' describes the addition of time, not a universal increase in diagnostic accuracy. The best technique depends on the clinical question. Standard 2D imaging remains central to routine obstetric assessment, while 3D and 4D can provide complementary information in selected applications. [1, 2, 13, 14]

Why both can produce strange-looking faces

Both rely on ultrasound data and are affected by fetal position, motion, placenta, fluid and acoustic access. 4D does not see through an obstruction. In fact, because it repeatedly acquires volumes, motion and acquisition trade-offs remain important.

Educational diagram of why 3D and 4D faces can look unusual. Educational illustration; not a diagnostic ultrasound image.
4D does not see through obstruction; both 3D and 4D inherit the same acoustic limits. Educational illustration; not a diagnostic ultrasound image.

Safety principles

3D and 4D techniques are based on diagnostic ultrasound. AIUM and FDA emphasize medically appropriate, prudent use, qualified operators and minimizing unnecessary exposure. FDA discourages additional ultrasound exposure solely for keepsake purposes outside medically indicated examinations. [3, 4, 5, 15]

Which is better for a physical 3D representation?

A physical model requires spatial geometry, so a suitable 3D volume is the essential source. A 4D sequence contains repeated 3D volumes, from which an appropriate frame or volume may be selected. Model quality depends more on source volume quality and reconstruction than on the marketing label '3D' or '4D'.

Educational infographic comparing 2D, 3D and 4D ultrasound side by side. Educational illustration; not a diagnostic ultrasound image.
2D, 3D and 4D ultrasound: a side-by-side comparison. Educational illustration; not a diagnostic ultrasound image.

Medical disclaimer

This article is intended for educational purposes only and does not provide medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional regarding your individual medical care. This content is based on peer-reviewed scientific literature and current clinical guidelines available at the time of publication. Every article requires physician review before publication.

Key Takeaways

  • Conventional 2D ultrasound produces real-time cross-sectional images.
  • 4D imaging repeats 3D volume acquisition rapidly enough to display motion.
  • Not as a general rule.
  • Both rely on ultrasound data and are affected by fetal position, motion, placenta, fluid and acoustic access.
  • 3D and 4D techniques are based on diagnostic ultrasound.

Frequently Asked Questions

Is 4D ultrasound a video?

It is a moving display created by repeatedly acquiring and displaying 3D volumes over time.

Is 4D automatically better than 3D?

No. It adds time, but the best method depends on the clinical question and image quality.

Can a 4D scan be used for a 3D model?

A 4D sequence contains repeated 3D volumes. A suitable volume may be selected for reconstruction if source quality is adequate.

References

  1. ACOG. Ultrasound Exams. American College of Obstetricians and Gynecologists. Standard obstetric ultrasound is commonly performed at 18-22 weeks; specialized techniques may include 3D ultrasound. https://www.acog.org/womens-health/faqs/ultrasound-exams
  2. ISUOG Practice Guidelines (updated): performance of the routine mid-trimester fetal ultrasound scan. Ultrasound Obstet Gynecol. 2022;59:840-856. https://www.isuog.org/resource/isuog-practice-guidelines-updated-performance-of-the-routine-mid-trimester-fetal-ultrasound-scan.html
  3. FDA. Ultrasound Imaging. U.S. Food and Drug Administration. Ultrasound does not use ionizing radiation; keepsake images are reasonable when produced during a medically indicated examination without additional exposure. https://www.fda.gov/radiation-emitting-products/medical-imaging/ultrasound-imaging
  4. AIUM. Prudent Clinical Use and Safety of Diagnostic Ultrasound. 2019. Supports prudent, medically appropriate use and attention to acoustic output and exposure time. https://www.aium.org/resources/official-statements/view/prudent-clinical-use-and-safety-of-diagnostic-ultrasound
  5. AIUM. Prudent Use and Safety of Diagnostic Ultrasound in Pregnancy. Official statement. https://www.aium.org/resources/official-statements/obstetric-ultrasound
  6. NHS. 20-week screening scan. The anomaly scan is usually performed between 18 and 21 weeks and assesses fetal anatomy and growth. https://www.nhs.uk/pregnancy/your-pregnancy-care/20-week-scan/
  7. MedlinePlus. Fetal development. U.S. National Library of Medicine. https://medlineplus.gov/ency/article/002398.htm
  8. Connor A, Matthew J, Chung E, Wright R, Rutherford MA. Factors influencing the successful acquisition and quality of three-dimensional souvenir obstetric ultrasound facial images: a narrative review and quantitative evaluation. Ultrasound. 2026. PMID: 42294041. DOI: 10.1177/1742271X261436619. DOI: 10.1177/1742271X261436619 PMID: 42294041 Source
  9. Accuracy and repeatability of fetal facial measurements in 3D ultrasound: A longitudinal study. Early Hum Dev. 2024. PMID: 38701668. DOI: 10.1016/j.earlhumdev.2024.106021. DOI: 10.1016/j.earlhumdev.2024.106021 PMID: 38701668 Source
  10. Three-dimensional sonographic visualization of the fetal face. AJR Am J Roentgenol. PMID: 9456969. DOI: 10.2214/ajr.170.2.9456969. DOI: 10.2214/ajr.170.2.9456969 PMID: 9456969 Source
  11. Two- and three-dimensional sonographic assessment of the fetal face. 1. A systematic analysis of the normal face. Ultrasound Obstet Gynecol. PMID: 15027008. DOI: 10.1002/uog.984. DOI: 10.1002/uog.984 PMID: 15027008 Source
  12. Diagnostic evaluation of the fetal face using 3-dimensional ultrasound. Ultrasound Q. 2008;24:215-223. PMID: 19060688. DOI: 10.1097/RUQ.0b013e31819073c2. DOI: 10.1097/RUQ.0b013e31819073c2 PMID: 19060688 Source
  13. Three-dimensional and four-dimensional ultrasound applications in fetal medicine. Curr Opin Obstet Gynecol. 2009;21:167-174. PMID: 19996869. DOI: 10.1097/GCO.0b013e328329243c. DOI: 10.1097/GCO.0b013e328329243c PMID: 19996869 Source
  14. Role of 3-D ultrasound in clinical obstetric practice: evolution over 20 years. Ultrasound Med Biol. 2015. PMID: 25748522. DOI: 10.1016/j.ultrasmedbio.2014.12.009. DOI: 10.1016/j.ultrasmedbio.2014.12.009 PMID: 25748522 Source
  15. 3D/4D sonography - any safety problem. J Perinat Med. 2016;44:125-129. PMID: 26376219. DOI: 10.1515/jpm-2015-0225. DOI: 10.1515/jpm-2015-0225 PMID: 26376219 Source
  16. 4D ultrasound study of fetal facial expressions at 20-24 weeks of gestation. Int J Gynaecol Obstet. 2014;126:275-279. PMID: 24996686. DOI: 10.1016/j.ijgo.2014.03.036. DOI: 10.1016/j.ijgo.2014.03.036 PMID: 24996686 Source
  17. Fetal face shape analysis from prenatal 3D ultrasound images. Sci Rep. 2024. PMID: 38388522. PMCID: PMC10884000. DOI: 10.1038/s41598-023-50386-9. DOI: 10.1038/s41598-023-50386-9 PMID: 38388522 Source
  18. Three-dimensional ultrasonic images of normal fetus. Study of pregnancies 20-36 weeks; satisfactory recognizable images were reported particularly from 24-34 weeks. PMID page. PMID: 11601189 Source
  19. Three-dimensional ultrasonographic assessments of fetal development. PMID: 9469279. PMID: 9469279 Source
  20. Three-dimensional reconstruction of fetal abnormalities using ultrasonography and magnetic resonance imaging. PMID: 29656679. PMID: 29656679 Source

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