Ultrasound in Obstetrics

Definition

Ultrasound is a technique that uses sound waves to take a picture of the baby (fetus) in the uterus. Because it uses sound waves instead of radiation, ultrasound is safer than X-rays.

Description

Description

Ultrasound works by bouncing sound waves off the developing fetus. Echoes from the waves are converted into an image - called a sonogram - on a TV monitor. The technique is sometimes called sonography or sonar.

Ultrasound has become an increasingly important part of prenatal care, providing information that can guide a physician's care for a pregnant woman and improve the outcome of pregnancy.

Reasons To Use Ultrasound

Ultrasound has many uses during pregnancy, answering a variety of questions. Some of the most important are:

Suspected ectopic pregnancy. Ultrasound may be used to diagnose an out-of-place pregnancy that is located in the fallopian tubes or abdomen (outside of the uterus).

More than one baby. Ultrasound may be used to see if a woman is pregnant with twins, triplets, or a larger number of fetuses.

Verify due date. The size of the fetus, measured using ultrasound, helps doctors accurately estimate the baby's due date.

Evaluate fetal growth. If the uterus is growing faster or more slowly than expected, ultrasound can help determine the reason, such as too much amniotic fluid or poor fetal development.

Possible miscarriage. If there is bleeding in early pregnancy, or if the fetal heartbeat or movements seem to have stopped during pregnancy, ultrasound can help determine the status of the fetus.

Help perform other prenatal tests. If amniocentesis or chronic villus sampling are called for, doctors are guided by ultrasound in removing cells to test for certain possible birth defects.

Diagnose certain birth defects. Ultrasound pictures can be used to diagnose birth defects in body structure, such as missing limbs, and sometimes cleft lip and spina bifida. It can also diagnose certain malformations of internal organs, including the urinary tract. A special form of ultrasound called echocardiography can track the flow of blood through the fetal heart chambers, valves, and major blood vessels.

Check fetal well-being late in pregnancy. A test called the fetal biophysical profile adds several ultrasound checks to the non-stress test (a special monitoring of the fetal heartbeat that is suggested when a mother has diabetes or high blood pressure, or when she is overdue).

Help to select the delivery method. Ultrasound can be important in determining whether a cesarean section is needed in certain pregnancies, such as when the fetus is especially large or in an abnormal position, or when the placenta is blocking the exit from the uterus.

Methods

For pregnancy scanning, sound waves are usually sent by a handheld device called a transducer, rubbed back and forth across the pregnant woman's belly. For a clearer picture, the belly is covered with a gel and the woman is asked to have a full bladder while the test is performed.

Depending on the position of the fetus and the purpose of the ultrasound, the procedure may take as long as an hour. Ultrasound is painless but many women find that having a full bladder is quite uncomfortable.

Safety

Ultrasound has made pregnancies safer by eliminating the need for x-rays to "see" the fetus. Ultrasound has been used for many years, and many doctors believe so strongly in its safety that they suggest ultrasound during all pregnancies to check on the baby's growth and position. An ultrasound should only be used when medically indicated for reasons such as those above.

Questions to Ask Your Doctor

Is the use of an ultrasound indicated?

What will the ultrasound show?

Are there any risks involved?

Will the ultrasound be used in conjunction with other prenatal testing?

Is the procedure uncomfortable?

Is a full bladder necessary to have this procedure done?

Will the ultrasound be useful in determining the best delivery method?