Ultrasound scan: what to expect, common uses, safety and preparation

1. Introduction

An ultrasound scan is an imaging test that shows pictures of the inside of the body. These can be muscles, organs, blood vessels or a baby in the womb ^[1]. It uses high-frequency sound waves, too high for people to hear, and the pictures are called sonograms ^{[2, 4]}. The scan is usually done in hospitals or clinics ^[1] by a trained professional called a sonographer ^[2]. This article explains why ultrasound is used, how to prepare, what happens during the scan and what to know about safety. Your doctor decides whether you need a scan and what the result means.

2. How ultrasound works

A handheld device called a transducer sends sound waves into the body and picks up the echoes that bounce back from different tissues. A computer turns those echoes into images on a screen ^[2]. Gel is put on the skin because air would block the waves ^{[2, 3, 4]}. Since the pictures are made in real time, they can show movement, such as a heartbeat or blood flow ^[3]. A technique called Doppler ultrasound shows how fast and in which direction blood is flowing ^{[2, 4]}. Ultrasound works poorly on bone and on air-filled tissue such as the lungs ^[4].

3. Common uses

The NHS and MedlinePlus list uses such as ^{[1, 2]}:

• Looking into symptoms such as pain, swelling or a lump.
• Telling a cyst from a solid growth ^[2].
• Checking organs in the belly and pelvis, including the kidneys, thyroid and heart ^[2].
• Monitoring a condition, such as a thyroid problem.
• Guiding a procedure, such as an injection into a joint ^[1] or a biopsy, which collects fluid or tissue ^[2].
• Checking a baby's growth and development in pregnancy. A routine pregnancy scan is common between weeks 18 and 22, and extra scans may be advised for some pregnancies ^[2].

4. Getting ready

Follow the instructions from the hospital or clinic. Preparation depends on the body area. Some scans need none, and others need a full bladder or several hours without food ^{[1, 2]}. For a full bladder, you may be asked to drink several glasses of water shortly beforehand and avoid using the toilet ^[1]. You may need to remove jewellery or piercings near the area being scanned, and you can ask for a chaperone, who can be someone you know or a member of staff ^[1].

5. What happens during the scan

The scan usually takes 10 to 45 minutes but can take longer ^[1]. You may need to undress or change into a gown, or only move clothing aside. There are three main types ^[1]:

• External scan: gel is spread on the skin and the probe is moved over it. You may be asked to change position. The gel is wiped off afterwards.
• Internal scan: a tube-shaped probe is placed in the vagina or the rectum (the bottom). The probe is covered with a latex sleeve and lubricant, so tell staff if you have a latex allergy, as an alternative can be used. You can ask to put in the probe yourself, and you can ask for the scan to stop at any time.
• Endoscope-based scan: a probe on a thin tube is passed into the food pipe to look at structures such as the heart or stomach.

6. Safety

The NHS says ultrasound uses sound waves, not radiation like X-rays or CT ^[1]. MedlinePlus says it is generally considered safe when done correctly by trained sonographers ^[2]. The FDA says ultrasound has been used for more than 20 years and has an excellent safety record. Because it uses no ionizing radiation, it is useful for people, including women of childbearing age, who might otherwise need a radiation-based scan ^[3].

Ultrasound is not completely without effect. The FDA says it can slightly warm tissue and can sometimes make tiny gas bubbles in fluids or tissues, and that long-term effects are not fully known. Risks may rise with unnecessary long exposure or when untrained people use the equipment ^[3]. For this reason, the FDA and NIBIB discourage non-medical uses, such as keepsake baby videos, and say scans should be done when medically needed ^{[3, 4]}. The FDA also advises that home fetal heart monitors should be used only by trained providers when needed ^[3].

MedlinePlus lists some reasons for extra scans in pregnancy, such as reduced baby movement, ongoing belly pain or a high-risk pregnancy ^[2]. Scans can also be 3D, or 4D (3D with movement), and these are more often used in the third trimester ^[2]. The FDA says 3D scans can show some facial features and parts such as fingers and toes ^[3].

7. Results

Results may be given at the end of the appointment or may take a few weeks ^[1]. The results go to the doctor who referred you, who may arrange a follow-up. Further tests are sometimes needed. If you have not heard anything after a few weeks, contact the specialist or your GP surgery ^[1]. Routine pregnancy scan reports are usually added to your maternity notes ^[1].

MedlinePlus adds that a normal pregnancy scan suggests normal growth, but it does not guarantee a healthy baby, since not all conditions show on ultrasound. An abnormal result does not always mean a serious problem, and your doctor may recommend more testing ^[2].

8. When to see a doctor

Talk to a doctor about pain, swelling, a lump or other symptoms that need looking into, and about any questions regarding your pregnancy scans. Contact your referring doctor if you have not heard about your results after a few weeks ^[1]. In pregnancy, speak to your midwife or doctor promptly if you have bleeding, severe belly pain or you notice your baby moving much less than usual.

In an emergency, call your local emergency number (112 in India, 911 in the United States).

9. Conclusion

Ultrasound is a common test that makes live pictures with sound waves rather than radiation. It is helpful for symptoms, for guiding procedures and for pregnancy care. Follow the preparation steps, tell staff about allergies such as latex, and have scans only when they are medically needed. Your doctor decides what the findings mean and what comes next.