Risks

Diagnostic ultrasound is a safe procedure that uses low-power sound waves. There are no known risks.

Ultrasound is a valuable tool, but it has limitations. Sound doesn’t travel well through air or bone, so ultrasound isn’t effective at imaging body parts that have gas in them or are hidden by bone, such as the lungs or head. To view these areas, your doctor may order other imaging tests, such as CT or MRI scans or X-rays.

How you prepare

Most ultrasound exams require no preparation. However, there are a few exceptions:

For some scans, such as a gallbladder ultrasound, your doctor may ask that you not eat or drink for a certain period of time before the exam.

Others, such as a pelvic ultrasound, may require a full bladder. Your doctor will let you know how much water you need to drink before the exam. Do not urinate until the exam is done.

Young children may need additional preparation. When scheduling an ultrasound for yourself or your child, ask your doctor if there are any specific instructions you’ll need to follow.

3D and 4D ultrasound scans

3D scans show still pictures of your baby in three dimensions. 4D scans show moving 3D images of your baby, with time being the fourth dimension.It’s natural to be really excited by the prospect of your first scan. But some mums find the standard 2D scans disappointing when all they see is a grey, blurry outline. This is because the scan sees right through your baby, so the photos show her internal organs.With 3D and 4D scans, you see your baby’s skin rather than her insides. You may see the shape of your baby’s mouth and nose, or be able to spot her yawning or sticking her tongue out.

3D and 4D scans are considered as safe as 2D scans, because the images are made up of sections of two-dimensional images converted into a picture. However, experts do not recommend having 3D or 4D scans purely for a souvenir photo or recording, because it means that you are exposing your baby to more ultrasound than is medically necessary. Some private ultrasounds can be as long as 45 minutes to an hour, which may be longer than recommended safety limits.3D and 4D scans may nonetheless provide more information about a known abnormality. Because these scans can show more detail from different angles, they can help in the diagnosis of cleft lip. This can help doctors to plan treatment to repair a baby’s cleft lip after birth.

3D scanning can also be useful to look at the heart and other internal organs. As a result, some fetal medicine units do use 3D scans, but only when they’re medically necessary.There’s no evidence to suggest that the scans aren’t safe, and most mums-to-be gain reassurance from them. Nonetheless, any type of ultrasound scan should only be performed by a trained professional, for as short a time and at the lowest intensity, as possible.

If you’d like a 3D or 4D scan you’ll probably need to arrange it privately and pay a fee. The clinic may also give you a recording of the scan on DVD, though this is likely to cost extra.The special transducers and software required to do 3D and 4D scans are expensive. There are few clear medical benefits, and experts say they should only be done if there’s a medical need. So it’s unlikely that these scans will replace normal 2D scans used for routine maternity care in the NHS.

If you decide to have one, the best time to have a 3D or 4D scan is when you’re between 27 weeks and 32 weeks pregnant.

Before 27 weeks your baby has very little fat under her skin, so the bones of her face will show through. After 32 weeks, your baby’s head may go deep down in your pelvis, so you may not be able to see her face.If you’re pregnant with twins or more, it’s best to have a 3D or 4D scan earlier rather than later, when you’re about 27 weeks pregnant, so you can get a clearer view of each baby.