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Pregnancy and Childbirth

What is Ultrasound and How is it Used?

What is ultrasound?

Ultrasound (or "ultrasonography") is a medical diagnostic tool that uses high frequency sound waves to produce images of structures within the body. This test is commonly used during pregnancy to evaluate the fetus and the mother. Ultrasound allows your doctor to evaluate both structural aspects (i.e. whether the fetus' body is developing normally) and functional aspects (i.e. whether the fetus and its organs are operating as they should). Because it is a "real time" imaging procedure, doctors can examine such processes as body motion, cardiac activity and breathing movements.

When in pregnancy is ultrasound performed?

Ultrasound may be performed at any time during a pregnancy depending on the indications (to be discussed later in this article).

What are we looking for?

First Trimester
In the first trimester (first 3 months), ultrasound is primarily performed to evaluate vaginal bleeding, assess the age of the fetus, and confirm that the fetus is alive. Chorionic villus sampling, a way to evaluate the genes of the fetus (described in more detail below), is also performed in the first trimester. Ultrasound is used to assist in this procedure.

Second Trimester
In the second trimester (third through sixth months) ultrasound is generally performed to evaluate the fetus for anatomic or structural abnormalities. Abnormalities may be suspected because of a prior abnormal pregnancy, or because of a blood test. The best time to perform a second trimester ultrasound for structural anomalies is between 17 and 20 weeks of gestation. Genetic amniocentesis, the removal of a small amount of amniotic fluid from the womb (described in more detail below), may also be performed during the second trimester using ultrasound guidance.

Third Trimester
Third trimester (sixth through ninth months) ultrasonography is performed to evaluate the fetus' growth, and to confirm its size if your doctor is concerned that it may be too small or too large. Previously diagnosed abnormalities can be reevaluated and followed in the third trimester. Amniocentesis to evaluate the maturity of the fetus is performed in the late third trimester. A weight assessment can also be performed in the late third trimester to help your doctor plan the optimal method of delivery.

Are there risks?

Ultrasound has been performed in the United States since the late 1960s and its safety has been studied for thirty years. To date, no adverse effects of ultrasound have ever been demonstrated in humans.

Who performs an ultrasound?

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