What does it add compared with two-dimensional?
In assessing the structure of the womb
This is where three-dimensional ultrasound is strongest. With two-dimensional ultrasound it is almost impossible to obtain a view of the womb from above. Three-dimensional ultrasound, by showing the womb in three planes at once, reveals the full anatomy of both the inner cavity and the outer border.
The difference in figures: in diagnosing congenital differences of the womb, the accuracy was found to be 97.1% with three-dimensional ultrasound and, with two-dimensional, 51.4% on first assessment and 82.9% in experienced hands.
This difference matters particularly in people with infertility and recurrent pregnancy loss: its greatest advantage is being able to distinguish without error between a septum inside the womb and a double womb — because the treatment of the two is entirely different.
It is also more sensitive than two-dimensional ultrasound in showing adhesions inside the womb, polyps and the position of fibroids.
The recorded image can be reviewed later
The volume data acquired in three-dimensional ultrasound can be stored digitally. This means the image can be reviewed from different angles and the measurements repeated even after you have left. This makes the assessment less dependent on the person performing it.
The baby's brain and spine
- In examining the brain: where it is difficult to obtain a two-dimensional image, it makes it possible to obtain sections aligned in three exactly perpendicular planes. Because thicker sections can also be taken, image quality improves markedly.
- In examining the spine: reconstructing the bones of the spine from above increases diagnostic accuracy in assessing an open spinal defect.
Is ultrasound safe?
Ultrasound involves no radiation and is regarded as safe in clinical use. To date there is no independently confirmed study showing otherwise.
Even so, because it is known that high-energy sound waves can produce heat and mechanical effects in tissues, international safety principles are followed.
The ALARA principle
ALARA means "as low as reasonably achievable". Under it, the lowest power sufficient to make the diagnosis should be used and the scan kept as short as possible.
Extra care in the use of Doppler
- Doppler (colour flow) studies emit considerably more energy than standard grey-scale imaging.
- When Doppler is used in pregnancy, the thermal index shown on the screen must be kept below a certain limit and the examination time limited — generally not exceeding 5–10 minutes.
- In the first 11 weeks of pregnancy, Doppler should not be used unless there is a medical necessity.
On modern machines the thermal and mechanical indices must be continuously visible on the screen.
About keepsake ultrasound
On this subject what the guidelines say needs to be passed on as it stands:
Three- and four-dimensional ultrasound can give families lovely images showing the baby's face. Against that, the recommendation of the international ultrasound society (ISUOG) is clear: ultrasound should not be performed on its own solely to please the parents or to obtain a commercial keepsake image.
The reasoning is this: any scan without a medical purpose violates the ALARA principle and exposes the baby to unnecessary sound energy.
This does not mean that it is wrong to share images obtained during a medical examination. What is being said is this: a scan should not be carried out purely to obtain images.
Who should perform it?
Guidelines require the person performing the scan to meet the following criteria:
- To be trained in diagnostic ultrasound and in safety
- To perform fetal ultrasound regularly
- To take part in continuing medical education
- To have a referral pathway in place for doubtful or abnormal findings
- To carry out quality audit regularly
Frequently Asked Questions
Is four-dimensional ultrasound better than two-dimensional?
They are used for different jobs. The real value of three- and four-dimensional ultrasound is that it shows what two-dimensional cannot: the view of the womb from above, exactly aligned sections in examining the brain, and reconstruction of the spine. Routine screening, on the other hand, is done with two-dimensional ultrasound.
Why is three-dimensional requested for the structure of the womb?
Because the difference is large. In diagnosing congenital differences of the womb, the accuracy is 97.1% with three-dimensional; with two-dimensional it is 51.4% on first assessment and 82.9% in experienced hands. Distinguishing a septum inside the womb from a double womb is particularly critical — the treatment of the two is entirely different, and the distinction matters in infertility and recurrent pregnancy loss.
Does ultrasound harm the baby?
Ultrasound involves no radiation and is regarded as safe in clinical use; there is no independently confirmed study showing otherwise. Even so the ALARA principle is applied: the lowest power sufficient to make the diagnosis is used and the scan is kept as short as possible.
Is extra care needed with Doppler?
Yes. Doppler studies emit considerably more energy than standard imaging. For this reason the thermal index is kept below a certain limit in pregnancy and the time is limited to generally not more than 5–10 minutes. In the first 11 weeks of pregnancy Doppler should not be used unless there is a medical necessity.
Can I have an ultrasound just to see my baby's face?
That is not what the guidelines recommend. The recommendation of the international ultrasound society is clear: ultrasound should not be performed on its own solely to please the parents or to obtain a commercial keepsake image. The reasoning is that any scan without a medical purpose violates the ALARA principle and exposes the baby to unnecessary sound energy. This does not mean that images obtained during a medical examination cannot be shared.
Can the images be reviewed again later?
Yes, and this is an important advantage of three-dimensional ultrasound. The volume data acquired can be stored digitally; the image can be reviewed from different angles and the measurements repeated even after you have left. This makes the assessment less dependent on the person performing it.
Who should perform the examination?
Guidelines look for the following criteria: being trained in diagnostic ultrasound and in safety, performing fetal ultrasound regularly, taking part in continuing medical education, having a referral pathway in place for doubtful findings, and carrying out quality audit regularly.
Sources
- ISUOG Practice Guidelines — Routine mid-trimester fetal ultrasound examination. Ultrasound safety, the ALARA principle and the recommendation on keepsake use.
- ISUOG Practice Guidelines — Updated performance of the 11–14-week ultrasound scan and Doppler velocimetry in obstetrics. Thermal and mechanical indices, the duration of Doppler and its use before week 11.
- ISUOG Practice Guidelines — targeted neurosonography. The contribution of the three-dimensional approach to assessment of the fetal brain and spine.
- ESHRE/ESGE consensus and the ESHRE Guideline on Recurrent Pregnancy Loss — the accuracy of three-dimensional ultrasound against two-dimensional in diagnosing differences of the womb.
The information on this page is based on the national and international guidelines listed above. The page is reviewed whenever those guidelines are updated.
Practice and Contact Details
The information on this page is general. Please speak to your doctor about your own situation.
- DoctorOp. Dr. Murat Alpay — Specialist in Obstetrics and Gynaecology
- AddressOp. Dr. Murat Alpay Practice, Tekelioğlu Cd. No:51 B Kat:2, Filo Apt., 07160 Muratpaşa / Antalya
- Telephone0505 351 77 88
- HoursMonday – Saturday 09:00 – 18:00 · Closed on Sunday