Ultrasound was developed during World War I when high frequency sound waves were used to detect enemy submarines. The form of ultrasound used in pregnancy testing uses intermittent sound waves. The sound waves are directed into the woman’s abdomen, with an outline of the placenta, and other structures involved in the pregnancy transmitted to a video screen. A sonogram is often used to determine fetal position, to estimate the maturity of the baby, is to confirm a multiple pregnancy. In addition, the location of the placenta can be pinpointed when placenta previa (low implanted placenta) is suspected. Ultrasound is also used to visualize the baby and placenta when amniocentesis or CVS is being performed. Since X-rays are now considered dangerous in developing babies, ultrasound is used instead.
Many doctors use ultrasound routinely to determine the due time. When the test is performed between the fourteenth and twentieth weeks, it is accurate to within 1 week before or after the estimated date. Later in pregnancy, and especially after the thirty-second week, it is not as accurate at determining due date of variations in fetal growth. In a higher-risk pregnancy, accurate due date is important for making sure that the infant is delivered at the best time. Routine ultrasound is usually done during the sixteenth and nineteenth weeks of pregnancy.
Ultrasound can also be directed in a continuous wave to the baby’s heart rate. This is done during routine examinations using a doptone. Most often, it is done during labor using an electronic fetal monitor.
This type of profile includes fetal movements, muscle tone, amount of amniotic fluid, and fetal breathing movements. The test is usually done in higher risk pregnancies to assure fetal well-being and to determine the best time for delivery.
Diagnostically, ultrasound is preferred over X-rays. However, many doctors now use ultrasound routinely during labor, as well as recommending one or more sonograms during pregnancy. The same as other procedures, ultrasound should not be used indiscriminately, and you have the legal right to refuse it. A 6-year study by the National Institute of Child Health and Human Development, a division of NIH, concluded that no benefit is derived from the routine use of ultrasound in low-risk pregnancies. This study, the largest ever conducted, found that prenatal outcome was not improved by routine screening when compared with the selective use of ultrasonography based on the caregiver’s judgment. The investigators estimated that $1 billion a year could be saved if sonograms are limited to higher-risk pregnancies and other cases in which it is medically indicated.
If your caregiver requests a sonogram and you do not have insurance to cover the cost, ask if the procedure is medically necessary and what information your caregiver hopes to receive. Also, ask if the information will change your care. In addition, if you are going to have a sonogram, you may want to ask about the credentials of the person performing and interpreting the test. Does that person have training or certification in ultrasonography? The FDA has guidelines regarding the intensity of the machines and the amount of time a fetus should be exposed.
Because so much information can be gained about the fetus through diagnostic ultrasound, and because studies have not shown any long-term effects on babies, many doctors feel strongly that the benefits of ultrasound outweigh the risks. Others, however, oppose its use without a medical indication, since routine screening of all women is still not recommended by the NIH or the American College of Obstetricians and Gynecologists.