Ultrasound examination, also called sonography or diagnostic medical sonography, is an imaging method that uses high-frequency sound waves to produce precise images of structures within your body. The images produced during an ultrasound examination often provide information that is valuable in diagnosing and treating a variety of diseases and conditions.
Most ultrasound examinations are done using a sonar device outside of your body, though some ultrasound examinations involve placing a device inside your body. Despite its valuable uses, ultrasound cannot provide images of all areas of your body—but there are several other imaging alternatives.
Why it's done
You may need to undergo an ultrasound for a variety of reasons. Ultrasound may be used, among other things, to:
- Evaluate a fetus.
- Diagnose gallbladder disease.
- Evaluate flow in blood vessels.
- Guide a needle biopsy.
- Guide the biopsy and treatment of a tumor.
- Check your thyroid gland.
- Study your heart.
- Diagnose some forms of infection.
- Diagnose some forms of cancer.
- Reveal abnormalities in the scrotum and prostate.
- Evaluate abnormalities of the muscles and tendons.
How you prepare
Reviewed 12/15/2022
Pregnancy: How baby develops
MONTH 1
The heart and lungs begin to form. Your baby is just a tiny embryo at this stage.
MONTH 2
All the baby's major body organs are beginning to develop. The ears, fingers and toes are also beginning to form.
At the six-week mark, you may be able to hear the baby's heartbeat during an ultrasound. By the end of the second month, the baby is about an inch long.
MONTH 3
Soft nails are beginning to form on the fingers and toes. Tiny buds have appeared that will later become baby teeth.
By the end of this month, the baby is about 3 inches long and weighs about an ounce.
MONTH 4
The baby moves, kicks, swallows and can hear.
By the end of the fourth month, the baby is around 6 inches long and weighs about 4 ounces.
MONTH 5
The baby now sleeps and wakes at regular intervals, and his or her skin is covered with fine, soft hair.
At the end of this month, the baby is about 10 inches long and weighs around 1 pound.
MONTH 6
At this stage, the lungs still aren't ready for life outside the womb.
By the end of the sixth month, the baby is about 12 inches long.
MONTH 7
Responsive to light and sound, the baby can now open and close his or her eyes. Moms may notice a lot of activity in the womb as the baby kicks and stretches.
MONTH 8
Your baby is gaining weight rapidly.
By the end of the eighth month, the baby is about 14 to 18 inches long and weighs around 4 to 5 pounds.
MONTH 9
Halfway through the month your baby will be full-term. To get ready for birth, the baby will usually turn head down and move down into the pelvic area.
HOW WILL YOU KNOW YOU'RE IN LABOR?
Sources: American College of Obstetricians and Gynecologists; American Pregnancy Association; Office on Women's Health
Sources
- American College of Obstetricians and Gynecologists. "How Your Fetus Grows During Pregnancy." https://www.acog.org/womens-health/faqs/how-your-fetus-grows-during-pregnancy?utm_source=redirect&utm_medium=web&utm_campaign=otn.
- American Pregnancy Association. "Fetal Development – How to Calculate Gestational Age." https://americanpregnancy.org/healthy-pregnancy/while-pregnant/fetal-development/.
- American Pregnancy Association. "Second Trimester: Fetal Development." https://americanpregnancy.org/healthy-pregnancy/pregnancy-health-wellness/second-trimester/.
- American Pregnancy Association. "Third Trimester of Pregnancy: Fetal Development." https://americanpregnancy.org/healthy-pregnancy/pregnancy-health-wellness/third-trimester/.
- Office on Women's Health. "Stages of Pregnancy." https://www.womenshealth.gov/pregnancy/youre-pregnant-now-what/stages-pregnancy.
How you prepare for an ultrasound depends on which areas of your body need evaluation. Some ultrasound exams require no preparation. Others require that you forgo food and liquids for up to 6 hours before the exam. Still others require that you not urinate before the exam to ensure that your bladder will be full, allowing better visualization of the uterus, ovaries or prostate.
When scheduling your ultrasound, ask your doctor for specific instructions for your particular exam.
What you can expect
During an ultrasound exam, you usually lie on an examination table. A small amount of gel is applied to your skin. The gel helps eliminate the formation of air pockets between the ultrasound and your body. During the exam, a technician trained in ultrasound imaging (sonographer) presses a small handheld device (transducer), about the size of a bar of soap, against your skin over the area of your body being examined, moving from one area to another as necessary.
Based on the same principles as sonar, a technology used to detect underwater objects, the transducer generates and receives high-frequency sound waves that cannot be heard by the human ear.
Though the majority of ultrasound exams are performed with a transducer on your skin, some ultrasounds are done inside your body (invasive ultrasounds). For these exams, the transducer is attached to a probe that is inserted into a natural opening in your body. Examples of these exams include:
- Transesophageal echocardiogram: The transducer is inserted into your esophagus to obtain images of the nearby heart. Such exams are typically performed along with sedation.
- Transrectal ultrasound: A small, specialized transducer is inserted into a man's rectum to view his prostate.
- Transvaginal ultrasound: A small, specialized transducer is inserted into a woman’s vagina to view her uterus and ovaries.
Ultrasound is usually a painless procedure. However, you may experience some mild discomfort as the sonographer guides the transducer over your body, especially if you are required to have a full bladder. A typical ultrasound exam takes from 30 minutes to an hour.
Results
When your exam is complete, the sonographer and a radiologist generally view the ultrasound images on film or on a computer monitor. The radiologist analyzes the images and sends a report of the findings to your doctor.
If your ultrasound exam is for an urgent medical condition, your doctor should receive your results immediately. Otherwise, you should have your results within a few days.
Safety
Diagnostic ultrasound is a safe procedure that uses low-power sound waves. There are no direct risks from a diagnostic ultrasound exam. Rarely, higher power sound waves can be used for treatment purposes to heat and even destroy some types of tissue or tumors.