What is prenatal ultrasound (ultrasonography)?
In ultrasonography, or ultrasound, high-frequency sound waves are sent through your abdomen by a device called a transducer. The sound waves are recorded and changed into video or photographic images of your baby. The ultrasound can be used during pregnancy to show images of the amniotic sac, placenta, and ovaries.
The idea for ultrasonography came from sonar technology, which makes use of sound waves to detect underwater objects. Ultrasound might be used with other diagnostic procedures, such as amniocentesis, or by itself.
Are there any side effects to prenatal ultrasound?
Studies have shown ultrasound is not hazardous. There are no harmful side effects to you or your baby. In addition, ultrasound does not use radiation, as X-ray tests do.
When is an ultrasound performed during pregnancy?
Most prenatal ultrasound procedures are performed on the surface of the skin, using a gel as a conductive medium to aid the quality of the image. However, a transvaginal ultrasound is performed using a probe that is inserted into the vaginal canal. This method of ultrasound produces an image quality that is greatly enhanced.
A transvaginal ultrasound may be used early in pregnancy to determine how far along you are in your pregnancy (gestational age) if this is uncertain or unknown. It may also be used to get a clearer view of the uterus or ovaries if a problem is suspected.
An ultrasound is generally performed for all pregnant women at 20 weeks gestation. During this ultrasound, the doctor will evaluate if the placenta is attached normally, and that your baby is growing properly in your uterus. The baby's heartbeat and movement of its body, arms, and legs can also be seen on the ultrasound.
If you wish to know the gender of your baby, it can usually be determined at 20 weeks. Be sure to tell the ultrasound doctor whether or not you want to know the gender of your baby. Please understand that ultrasound is not a foolproof method of determining your baby's gender. There is a chance that the ultrasound images can be misinterpreted. An ultrasound might be performed earlier in your pregnancy to determine:
- Presence of more than one fetus
- Your due date or gestational age (the age of the fetus)
Later in pregnancy, ultrasound might be used to determine:
- Fetal well-being
- Placenta location
- Amount of amniotic fluid around the baby
- Position of the baby
- Baby's expected weight
Major anatomical abnormalities or birth defects can show up on an ultrasound. Even though ultrasound is safe for mother and baby, it is a test that should be done only when medically necessary. If you have an ultrasound that is not medically necessary (for example, to simply see the baby or find out the baby's sex), your insurance company might not pay for the ultrasound.
Before the test
There is no special preparation for the ultrasound test. Some doctors require you to drink 4 to 6 glasses of water before the test, so your bladder is full. This will help the doctor view the baby better on the ultrasound. You will be asked to refrain from urinating until after the test. You will be allowed to go to the bathroom right after the test has been completed. You might be asked to change into a hospital gown.
During the test
You will lie on a padded examining table during the test. A small amount of water-soluble gel is applied to the skin over your abdomen. The gel does not harm your skin or stain your clothes.
A small device, called a transducer, is gently applied against the skin on your abdomen. The transducer sends high-frequency sound waves into the body, which reflect off internal structures, including your baby. The sound waves or echoes that reflect back are received by the transducer and transformed into pictures on a screen. These pictures can be printed out.
There is virtually no discomfort during the test. If a full bladder is required for the test, you might feel some discomfort when the probe is applied. You might be asked to hold your breath briefly several times. The ultrasound test takes about 30 minutes to complete.
After the test
The gel will be wiped off your skin. Your doctor will discuss the test results with you. Your ultrasound test is performed by a registered, specially trained technologist and interpreted by a board-certified physician. Your doctor will review the test results with you at your next visit.