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MIDWIFERY TODAY E-NEWS
a publication of Midwifery Today, Inc.
Volume 5 Issue 17 August 20, 2003
Ultrasound: high-frequency sound waves that travel at 10 to 20 million cycles per second. The pattern of echo waves creates a picture of tissue and bone.
In 1987, UK radiologist H.D. Meire, who had been performing pregnancy scans for 20 years, commented, "The casual observer might be forgiven for wondering why the medical profession is now involved in the wholesale examination of pregnant patients with machines emanating vastly different powers of energy which is not proven to be harmless to obtain information which is not proven to be of any clinical value by operators who are not certified as competent to perform the operations" (1).
Routine prenatal ultrasound (RPU) actually detects only between 17 and 85 percent of the 1 in 50 babies who have major abnormalities at birth (2,3).
RPU can identify a low-lying placenta (placenta previa). However, 19 of 20 women who have placenta previa detected on an early scan will be needlessly worried: the placenta will effectively move up without causing problems at the birth. Furthermore, detection of placenta previa by RPU has not been found to be safer than detection in labor (4).
The American College of Obstetricians has concluded that "in a population of women with low-risk pregnancies, neither a reduction in perinatal morbidity and mortality nor a lower rate of unnecessary interventions can be expected from routine diagnostic ultrasound. Thus ultrasound should be performed for specific indications in low-risk pregnancy (5).
Effects of ultrasound include cavitation, a process wherein the small pockets of gas that exist within mammalian tissue vibrate and then collapse. In this situation "...temperatures of many thousands of degrees Celsius in the gas create a wide range of chemical products, some of which are potentially toxic. These violent processes may be produced by microsecond pulses of the kind which are used in medical diagnosis." (American Institute of Ultrasound Medicine Bioeffects Report 1988). The significance of cavitation in human tissue is unknown.
Studies have suggested that these effects are of real concern in living tissues: *Cell abnormalities caused by exposure to ultrasound were seen to persist for several generations (6). *In newborn rats (similar stage of development as human fetuses at four to five months in utero), ultrasound can damage the myelin that covers nerves (7). *Exposing mice to dosages typical of obstetric ultrasound cased a 22% reduction in the rate of cell division and doubling of the rate of aptosis (programmed cell death), in the cells of the small intestine (8). *Two long-term randomized controlled trials comparing exposed and unexposed childrens' development at eight to nine years old found no measurable effect from ultrasound. However, the authors comment that intensities used today are many times higher than there were in 1979 and 1981 (9).
EXCERPTED FROM "Ultrasound Scans: Cause for Concern," by Sarah Buckley, MD, Midwifery Today Issue 64, also published in Nexux, Oct-Nov 2002.
1. Meire, HB (1987). "The Safety of Diagnostic Ultrasound," British J of Ob Gyn 94: 1121-22. 2. Ewigman, BG et al. (1993). "Effect of Prenatal Ultrasound Screening on Perinatal Outcome: RADIUS Study Group," New Eng J Med 329(12): 821-7. 3. Luck, CA (1992). "Value of Routine Ultrasound Scanning at 19 Weeks: a Four-Year Study of 8849 Deliveries," Brit Med J 34(6840): 1474-8. 4. Saari-Kemppainen, A., et al. (1990). "Ultrasound Screening and Perinatal Mortality: Controlled Trial of Systematic One-Stage Screening in Pregnancy. The Helsinki Ultrasound Trial," Lancet 336(8712): 387-89.
5. American College of Obstetricians and Gynecologists (ACOG) (August 1997). Practice Patterns: Evidence-Based Guidelines for Clinical Issues in Obstetrics and Gynecology. "Routine Ultrasound in Low-Risk Pregnancy." No. 5. 6. Liebeskind, D. et al. (1979). "Diagnostic Ultrasound: Effects on the DNAS and Growth Patterns of Animal Cells," Radiology 131(1): 177-84. 7. Ellisman, MH et al.,(1987). "Diagnostic Levels of Ultrasound May disrupt Myelination," Exper Neur 98(1): 78-92. 8. Brennan P et al. (1999). "Shadow of Doubt," New Scientist 12:23. 9. Salvesen KA et al. (1999). "Ultrasound in Pregnancy and Subsequent Childhood Non-Right-Handedness: A Meta-Analysis," Ultrasound Obstet Gyn 13(4): 241-6.
For the article in its entirety:
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A retrospective study to explore the associations of placenta previa with preterm delivery, growth restriction, and neonatal survival examined birth/infant death records from 22,368,235 singleton pregnancies. Previa-related births were by cesarean. Analyses were adjusted for year of delivery, maternal age, gravidity, education, prenatal care, marital status, and race/ethnicity. Placenta previa was recorded in 2.8 per 1000 live births. Neonatal mortality rate was 10.7 with previa compared with 2.5 per 1,000 among other pregnancies, but among preterm births, placenta previa was not associated with increased neonatal mortality. Babies born to women with placenta previa weighed less than babies born to women without placenta previa; compared with babies born to women without previa, the risk of death from placenta previa was lower among preterm babies of less than 37 weeks gestation. At 37 weeks the mortality rate was higher for babies born to women with placenta previa than for babies born to women without placenta previa.
Am J Obstet Gynecol. 2003 May; 188(5):1299-304.