Prenatal Ultrasound Health Article

Definition

Prenatal ultrasound is a procedure performed during pregnancy to obtain images of the fetus.

Description

A prenatal ultrasound, also known as a sonogram, is a procedure in which a tool called a transducer is placed on a woman's abdomen so that images of the fetus in the women's uterus can be viewed on a monitor. The most commonly used ultrasound produces a two-dimensional image of the fetus, although the technology exists to create a three-dimensional image as well. Electrical energy coming in to the transducer is converted to high-frequency sound waves. The sound waves reflect off of any structures they contact and return to the transducer and are converted back to electrical energy. Generally, more dense structures, like fetal bones, are seen as bright white images on the screen. Less dense tissue, like organs and fluid, shows darker on the screen. Gel placed on the woman's abdomen acts as a medium and allows for more rapid transmission of the sound waves and a better image.

There are many reasons an obstetrician may recommend an ultrasound for a pregnant woman. Some of these reasons include getting an accurate gestational age (dating) of the pregnancy, determining viability of a fetus (i.e., heartbeat), determining if any structural changes are present in the fetus, and determining if there are problems in the fetal environment. A prenatal ultrasound is performed by a health care professional, including an obstetrician, a radiologist, and a maternal-fetal medicine specialist. The American Institute of Ultrasound Medicine recommends that physicians performing ultrasound complete an approved residency program, a fellowship, or postgraduate training that includes three months and 500 supervised ultrasound procedures. An ultrasound technician often performs the initial measurements and, if needed, the physician reviews the procedure and obtains additional images. Ultrasounds are sometimes referred to as either basic (level 1) or comprehensive (level 2 or 3), depending on the quality of the equipment used, the amount and detail of the fetal anatomy studied, and the training of the person performing the procedure.

Most pregnant women in the United States have one prenatal ultrasound. There is some debate about when this ultrasound should take place. Early ultrasounds, in the first trimester of pregnancy, are the most accurate way to determine how far advanced a pregnancy is and to set an accurate due date. However, these early ultrasounds do not allow for a detailed study of the fetal anatomy for any changes in development. An anatomical study of the fetus is best performed at about 18–20 weeks gestation. Women who are at increased risk for birth defects, genetic conditions, or pregnancy complications may have multiple ultrasounds. Studies have shown, and the American Institute of Ultrasound Medicine Bioeffects Committee has concluded, that there is no association between prenatal ultrasounds using sound waves and an increased chance for birth defects or other pregnancy complications. Studies have also shown that there is significant psychological benefit to parents from having ultrasounds performed. Prenatal ultrasounds provide parents with reassurance that the fetus is developing normally, or identify problems that can be investigated further.