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Prenatal Ultrasound

Prenatal Ultrasound

Programs that perform this test

Hydrocephalus Program

What is an ultrasound?

An ultrasound scan is a diagnostic technique which 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 monitor normal fetal growth and verify the due date. Ultrasounds may be performed at various times throughout pregnancy for different reasons:

In the first trimester:

to establish the dates of a pregnancy
to determine the number of fetuses and identify placental structures
to diagnose an ectopic pregnancy or miscarriage
to examine the uterus and other pelvic anatomy
in some cases to detect fetal abnormalities

Mid-trimester: (sometimes called the 18 to 20 week scan)

to confirm pregnancy dates
to determine the number of fetuses and examine the placental structures
to assist in prenatal tests such as an amniocentesis
to examine the fetal anatomy for presence of abnormalities
to check the amount of amniotic fluid
to examine blood flow patterns
to observe fetal behavior and activity
to examine the placenta
to measure the length of the cervix
to monitor fetal growth

Third trimester:

to monitor fetal growth
to check the amount of amniotic fluid
as part of other testing such as the biophysical profile
to determine the position of a fetus
to assess the placenta

How is an ultrasound scan performed?

Although the specific details of each procedure vary slightly, generally, ultrasounds follow this process. Two types of ultrasounds can be 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. A woman may need to have a full bladder for abdominal ultrasounds in early pregnancy. This helps move the uterus into better view.
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.

Ultrasound images may be captured in still photographs or on video to document findings.

What are the risks and benefits of ultrasound?

There is no known evidence of any type of risk or danger to the fetus with ultrasound. The mother may experience some discomfort from the pressure of the ultrasound transducer or from having a full bladder, which may be needed in early pregnancy exams.

Ultrasound is a technique that is constantly being improved and refined. As with any test, results may not be completely accurate. However, ultrasound can provide valuable information for parents and healthcare providers to help manage and care for the pregnancy and fetus. In addition, ultrasound gives parents a unique opportunity to see their baby before birth, helping them to bond and establish an early relationship.


					Children's Hospital Boston is the primary pediatric teaching hospital of Harvard Medical School

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