An ultrasound scan is a diagnostic technique that uses high-frequency sound waves to create an image of the internal organs. A screening ultrasound is sometimes done during the course of a pregnancy to check for normal fetal growth and verify the due date. Ultrasounds may be performed at various times throughout pregnancy for different reasons. The reasons may vary depending on the trimester. For example:
In the first trimester, ultrasounds may be used to:
- establish the dates of a pregnancy
- determine the number of fetuses and identify placental structures
- diagnose an ectopic pregnancy or miscarriage
- examine the uterus and other pelvic anatomy
- detect fetal abnormalities
Mid-trimester (sometimes called the 18 to 20 week scan) ultrasounds may be used to:
- confirm pregnancy dates
- determine the number of fetuses and examine the placental structures
- assist in prenatal tests, such as an amniocentesis
- examine the fetal anatomy for presence of abnormalities
- check the amount of amniotic fluid
- examine blood flow patterns
- observe fetal behavior and activity
- examine the placenta
- measure the length of the cervix
- monitor fetal growth
Third trimester ultrasounds may be used:
- to monitor fetal growth
- to check the amount of amniotic fluid
- as part of the biophysical profile
- to determine the position of a fetus
- to assess the placenta
In addition to ultrasound, Beaumont's fetal imaging experts provide numerous imaging tests to assess fetal health.
How is an ultrasound scan performed?
Although the specific details of each procedure vary slightly, two types of ultrasounds are typically performed during pregnancy:
- Abdominal ultrasound—In an abdominal ultrasound, gel is applied to the abdomen and the ultrasound transducer glides over the gel on the abdomen to create the image.
- Transvaginal ultrasound—In a transvaginal ultrasound, a smaller ultrasound transducer is inserted into the vagina and rests against the back of the vagina to create an image. A transvaginal ultrasound produces a sharper image and is often used in early pregnancy.
There are several types of ultrasound imaging techniques. The most common is two dimensional, or 2-D. This gives a flat picture of one aspect of the image.
If more information is needed, a three-dimensional, or 3-D, ultrasound examination can be performed. This technique requires a special machine and a specially trained technician to perform the test. This procedure is beneficial because it allows the healthcare provider to see width, height and depth of images, which can be helpful in diagnosis. The 3-D images can also be captured and saved for later review.
The latest technology is 4-D ultrasound, which allows the health care provider to visualize the unborn baby moving in real time. With 4-D imaging, a three-dimensional image is continuously updated, providing a "live action" view. These images often have a golden color, which helps show shadows and highlights.
As with any test, ultrasound results may not be completely accurate. However, the test can provide valuable information for parents and health care providers to help manage and care for the pregnancy and fetus. An ultrasound can also give parents a unique opportunity to see their baby before birth, helping them to bond and establish an early relationship.
What are the risks and benefits of an ultrasound?
Fetal ultrasound has no known risks other than mild discomfort due to pressure from the transducer on the abdomen or in the vagina. No radiation is used during the procedure.
Transvaginal ultrasound requires covering the ultrasound transducer in a plastic/latex sheath, which may cause a reaction in patients with a latex allergy. If you have a latex allergy, let your health care provider know so they can use a non-latex sheath.
A fetal ultrasound is sometimes offered in nonmedical settings to provide keepsake images or videos for parents. While the ultrasound procedure itself may be safe, untrained personnel may give parents false assurances about their baby's well-being. Your ultrasound should be performed by trained medical personnel who can correctly interpret findings. Talk with your health care provider if you have questions.