University of Nebraska Medical Center

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What is an Ultrasound?

Ultrasound is a valuable tool performed alone or in conjunction with other prenatal diagnostic tests. As with all prenatal tests, a support person is welcome to accompany the pregnant woman.

This procedure uses high-frequency sound waves to create images on a video monitor. In most cases, the woman is asked to have a full bladder in preparation for this procedure. The woman lies on an exam table in a darkened room. In exams during early pregnancy a slender imaging device (vaginal probe) is guided gently into the woman's vagina. Second and third trimester exams are performed by moving a small rectangular imaging device (transducer) across the woman's stomach. A thin layer of warmed gel is spread across her stomach to improve the ultrasound image and allow movement of the transducer.

Early in pregnancy, the doctor uses these pictures to document implantation, fetal heartbeat, and movement. Later, it is also used to take specific measurements which aid in determining gestational age (age of the pregnancy starting at the onset of the last normal menstruation) and appropriate prenatal growth.

The presence of more than one fetus is usually apparent with this exam. Certain abnormalities of the fetal physical structure, umbilical cord, and placenta, may also be identified in later stages of pregnancy. Ultrasound is also essential to guide the physician in other diagnostic procedures.

Ultrasound has been used for over a quarter of a century. It has not been shown to have any adverse effects on the mother or baby. A normal ultrasound exam is reassuring but cannot rule out all forms of birth defects. The quality of the equipment, operator expertise, age and position of the fetus are important variables in its accuracy. In many cases it can assure both the patient and the doctor that fetal structures are present, but they cannot predict whether they will function properly.

Example of ultrasound

Human Genetics Laboratory