There are three types of ultrasound: scanning or sonograms (may be external or vaginal), doptones, and electronic fetal monitoring. Ultrasound is most often used in women who are considered high-risk, women above the a is a high frequency sound wave that vibrates at 10 to 20 million cycles per second, or 2-4 megahertz. Actual sound, that you hear, travels at 10-20 thousand cycles per second, or around 20 kilohertz. The return of the sound wave creates an image or echo of the tissue and bone composing the baby. Because bone is denser it appears whiter on the sonogram screen. Ultrasound is considered radiation, although not as intense as X-rays. Ultrasound is not limited to sonogram imaging. It is also used in hand-held Doppler’s and electronic fetal monitors, both of which detect fetal heart rate. Exposure time to the doppler may be significantly less than to ultrasound, however the frequency rate is much higher. In addition, the doppler is used, generally beginning around 10 weeks pregnancy, at each prenatal visit. Some women may also experience the use of internal vaginal ultrasound, especially during early pregnancy. Although the exposure to frequency levels may be the same, the scan is closer to the tissues, and the fetus is at a more vulnerable stage. Exposure time is often longest with the EFM. Women are generally hooked up to the monitor for 20 minute phases, although some women may be monitored continually.
Ultrasound may be used for a variety of reasons including pregnancy and gestational age confirmation, position of baby, position of placenta, and amniotic fluid amount. Ultrasounds may also be used to rule out multiples, abnormalities, small for dates babies, postdates (stress tests), and may be used in conjunction with other interventions.
The FDA recommends using ultrasound as diagnosis of pregnancy at 18 weeks, but warns against the routine use of ultrasound in pregnancy, stating the ultrasound should be used for diagnostic purposes only.
Although studies have been done on the risks of ultrasound use, they do not prove that ultrasound is harmful. Studies on animals, exposed to high levels of ultrasound, have displayed cellular changes. Additionally, ultrasound has been used in surgery and on a therapeutic basis because it can create cell lysis. Ultrasound is also known to cause cavitation—small pockets of gas, found in tissues, vibrate at a high rate, until the pockets collapse. These studies confirm that ultrasound, at least at increased exposure to very high frequency; can cause changes within the body. Randomized studies were done in Sweden and Norway showing and increased rate of left-handedness among children who had been exposed to frequent ultrasounds. Although the results are non-harmful, the increase in left-handedness suggests changes in the CNS and raises the question about long-term ultrasound effects which may not yet be visible. Other possible effects include delayed speech, miscarriage, and intrauterine growth restriction. These studies conclude that ultrasound use may be proven unsafe overtime if good randomized, controlled studies are conducted.
Ultrasound radiation may be avoided if women commit to having fewer ultrasounds and limit the exposure time to dopplers. Women who are not birthing with midwives can ask the ultrasonographer to perform the procedure as quickly and effectively as possible. Because we still have not had enough studies on the iatrogenic effects of ultrasound, it may be difficult to counsel women to avoid them altogether. However, it is apparent that the fetus is more vulnerable in early pregnancy and with long exposure time. Women might want to make note of the intensity of the exposure, duration, the manufacturer of the ultrasound equipment and the type of ultrasound used. It should also be suggested that they see and ultrasonographer who is highly experienced and comfortable with limiting the exposure time.