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Subject: misc.kids FAQ on Ultrasound

This article was archived around: 21 May 2006 04:22:34 GMT

All FAQs in Directory: misc-kids/pregnancy/screening
All FAQs posted in: misc.kids.info, misc.kids.pregnancy
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Archive-name: misc-kids/pregnancy/screening/ultrasound Posting-Frequency: monthly Last-Modified: February 16, 1995
------------------------------------------------------------ ------------------------------------------------------------ Misc.kids Frequently Asked Questions Ultrasound ===================================================================== Collection maintained by: Lynn Gazis-Sax (gazissax@netcom.com) To contribute to this collection, please send e-mail to the address given above, and ask me to add your comments to the FAQ file on AFP Screen and the Triple Screen. Please try to be as concise as possible, as these FAQ files tend to be quite long as it is. And, unless otherwise requested, your name and e-mail address will remain in the file, so that interested readers may follow-up directly for more information/discussion. For a list of other FAQ topics, ftp to the pub/usenet/misc-kids directory of rtfm.mit.edu or tune in to misc.kids.info. ===== Copyright 1995, Lynn Gazis-Sax. Use and copying of this information are permitted as long as (1) no fees or compensation are charged for use, copies or access to this information, and (2) this copyright notice is included intact. ==== ===================================================================== [NOTE: this is information collected from many sources and while I have strived to be accurate and complete, I cannot guarantee that I have succeeded. This is not medical advice. For that, see your doctor or other health care provider.] ===================================================================== Acknowledgements: Many people helped with the prenatal testing FAQs by advising about the best way to structure them, by contributing stories and information, or by reviewing versions of the FAQs. A list of acknowledgements can be found in the Prenatal Tests: Overview FAQ. ===================================================================== Note on language: When I first posted the questions for the prenatal testing FAQs, I used the term "birth defects" (except for question 7 of the Prenatal Testing Overview FAQ). Since I have been advised that this term may be offensive to people in the disabled community, I changed the wording of the final FAQs to use the word "disability," but most replies still reflect the original wording of the questions. ===================================================================== IV. Ultrasound 1. What are the different kinds of ultrasound and what can they detect? Ultrasound is high frequency sound waves which are used to visualize the fetus in utero. It works in a fashion similar to sonar. Ultrasound is used at a variety of different points in pregnancy to detect a variety of different things. Uses of ultrasound include: 1) to guide instruments for prenatal diagnosis (as, for example, the needle used in amniocentesis), 2) to confirm pregnancy, 3) to locate the baby (useful in ruling out ectopic pregnancy), 4) pregnancy dating, 5) to determine whether there is more than one baby, 6) to check the baby's growth, 7) to evaluate movement, tone, and breathing, 8) to identify sex (not as reliably as amniocentesis - don't paint the nursery based on this information), 9) to assess the amount of amniotic fluid, 10) as an adjunct to cervical cerclage or suture, 11) to look for molar pregnancies, 12) to determine the structure and position of the placenta (particularly useful if placenta previa is suspected), 13) to determine the cause of bleeding, 14) for fetal surgery, and 15) to confirm fetal death. Details on all of these uses can be found in _Prenatal Tests_ by Robin Blatt. Some places (e.g. India) are considering outlawing informing the parents of the sex of the child based on ultrasound, because of the tendency for female children to be aborted. The disabilities which ultrasound can detect are those which show up in the picture of the fetus, for example, anencephaly (by the twelfth week of pregnancy), spina bifida (by the twentieth week), disorders of the skeleton, central nervous system, heart, kidneys, or urinary tract. Ultrasound does *not* detect the severity of spina bifida, only whether it is present. ----------------------------------------- From Robbrenner@aol.com (Robert Brenner MD): Ultrasound can detect numerous structural defects. The list is too long to mention. ULTRASOUND CANNOT DETECT DOWN SYNDROME WITH ANY DEGREE OF ACCURACY. The American College of OBGYN states that routine ultrasound is not cost effective and does not influence neonatal outcome. Therefore, ultrasound is recommended only for indicated reasons such as bleeding, inaccurate dates, large or small for dates, family history or past history of structural birth defects that can be diagnosed by ultrasound, elevated AFP, abnormal triple screen, and for guidance at the time of amniocentesis. Late in pregnancy ultrasound is used to determine fetal well being, the amount of amniotic fluid, the position of the fetus, and to get an estimate of the size of the fetus. Ultrasound is routinely used to follow fetal growth in multiple gestations as well as fetuses who are small for gestational age. ----------------------------------------- From Franklin Tessler, MD, CM (FTessler@aol.com) [LGS: The part in square brackets is a correction of a paragraph which used to be in this FAQ - I removed the paragraph, but kept the correction, because I have seen posts asking about the meaning of the term "Level II ultrasound."] [The distinction between "Level I" and "Level II" ultrasound has nothing to do with the type of image produced. Rather, these terms have come to refer to the level of detail of an OB sonogram; that is, a routine "dating" sonogram would be considered Level I and a specialized or "targeted" exam would be considered Level II. In actual fact, professional ultrasound organizations such as the American Institute for Ultrasound in Medicine do *not* recognize the validity of these terms. Furthermore, all imaging ultrasound nowadays is "real time," and most Doppler ultrasound used to characterize blood flow during pregnancy is pulsed, rather than continuous. It is also untrue that ultrasound is only capable of detecting structural problems: for example, some cardiac arrhythmias (abnormal heart rhythms) can be detected sonographically.] Here is my suggested response: Ultrasound uses high-frequency sound waves to produce two-dimensional pictures of the body, including the fetus and its environment. (Three-dimensional ultrasound is being investigated.) Most of the time, these images are produced by placing a hand-held device called a transducer against the skin. (Sometimes, even clearer images can be produced by inserting a special transducer into a body cavity such as the vagina.) Most modern ultrasound equipment is capable of depicting moving structures such as the baby's heart, hence the term "real-time." Doppler ultrasound also uses sound waves, but instead of producing a picture, it shows the speed and direction of blood flowing through vessels. (A newer variant called color Doppler ultrasound depicts blood flow in pictorial form using color.) In the first trimester, ultrasound is most often used to determine whether a pregnancy is properly located within the uterus or is located in an abnormal position (ectopic pregnancy), or to confirm suspected miscarriage. This is also the most accurate time for dating pregnancy. First trimester ultrasound is often done using a vaginal approach. In the second trimester, ultrasound can be used to answer questions about and its surroundings, for example: How many babies are there? Where is the placenta located? Is the amount of amniotic fluid normal? How far along is the pregnancy? Ultrasound also is invaluable to guide interventional procedures such as amniocentesis. ----------------------------------------- 2. What can ultrasound not detect? ----------------------------------------- From Franklin Tessler, MD, CM (FTessler@aol.com) As far as detecting fetal abnormalities goes, several points need to be made: a) Not every problem can be diagnosed with ultrasound -- conditions which do not manifest as a structural or gross functional abnormality (such as a very abnormal heart beat) may be missed. b) Not every problem which can be detected will be diagnosed. For example, the basic ultrasound exam (for which there are published guidelines) does not include counting the baby's fingers and toes, even though it is possible to do so should it be necessary. c) The sensitivity of an ultrasound exam depends on a number of factors, such as the size and position of the fetus, the body habitus of the mother, the type of equipment used, and, most importantly, the skill and experience of the operator. Concerned parents-to-be may want to inquire politely about the training and experience of the person performing or interpreting their sonogram. d) Some problems (such as anencephaly) are more readily diagnosed than others (such as cleft palate). In the third trimester, ultrasound can be used to detect problems that may affect planning of delivery, such as intrauterine growth retardation (IUGR). As mentioned elsewhere, dating during this stage of pregnancy tends to be less accurate because biological variability is greater. ----------------------------------------- From Dr. T. Reynolds: Amazing claims are being made about nuchal fold thickness measurement as a screening technique for Down's but this technique is being performed in highly specialised teaching centres and there is as yet no evidence that the test could be carried out in 'lower-tech' local hospitals. ----------------------------------------- (The nuchal fold is on the back of the neck.) 3. How accurate is ultrasound, and what are possible sources of error? The accuracy of ultrasound for dating a pregnancy depends on at what point during the pregnancy the ultrasound is taken. Pregnancy dating is most accurate during the first half of pregnancy. Measurement of the sac at five to seven weeks gives an accuracy of plus or minus ten days. Measuring the crown-rump length gives an accuracy of plus or minus three days at seven weeks; this test can be used from the seventh to the fourteenth week. Between fourteen and twenty-six weeks, the measurement of the biparietal diameter of the baby's head, the femur length, and the head and abdominal circumference is used; the accuracy is plus or minus seven to ten days. Later in pregnancy, the accuracy declines, and may be plus or minus twenty-one days. ----------------------------------------- From Dr. T. Reynolds: The reason for this is that different babies grow at different rates and that all measurements are subject to inacccuracy because the object being measured is not linear (e.g. a babies head is not a sphere, it is an ellipsoid, so it is possible to get different slightly measurements depending on what position the baby lies in. ----------------------------------------- I haven't found many estimates of exactly how accurate ultrasound is at detecting disabilities, but there are both false negatives and false positives. The accuracy will vary depending on the experience of the person doing the ultrasound. The accuracy also varies with which condition is being detected. For Down Syndrome, it is very low. For anencephaly, on the other hand, it is highly effective. Some estimates: "The use of routine ultrasound, including a four-chamber view of the heart, can lead to the diagnosis of approximately 50 percent of major cardiac, kidney, and bladder abnormalities that would not be detected by maternal serum alpha-fetoprotein screening. When targetted ultrasound examination is performed by skilled ultrasonographers to detect malformations suspected on the basis of the history or the screening ultrasonogram, the sensitivity and specificity of this procedure are greater than 90 percent." (NEJM, 1/14/93, Prenatal Diagnosis) It is estimated that ultrasound can detect 81% of ectopic pregnancies (Brit Journal of Obst and Gyn, Dec 1988, Vol 95, pp 1253-1256). Ultrasound is most effective for gross structural abnormalities. It is highly effective for anencephaly. (Medical Intelligence. Chervenak et al. Advances in the Diagnosis of fetal defects.) ----------------------------------------- From Dr. T. Reynolds For spina bifida there is definitely evidence (but I can't remember where I saw it) that diagnostic accuracy is improved by having the AFP test: i.e. a high AFP result concentrates the mind of the ultrasonographer and they look for and often spot smaller neural tube defects. It is for this reason that some centres continued screening for spina bifida using AFP even when ultrasound arrived and certain quarters called for an end to the blood test because it was unnecessary duplication. ----------------------------------------- 4. What are the risks of ultrasound? This question turns out to be controversial. Some of the books which I consulted reassured that ultrasound has been used for decades with little risk, and that, while more studies could be done, the studies which have been done confirm its safety. "Although the effects of ultrasound are still being studied, no harmful effects to either the mother or the baby have been found in over 20 years of use. The long-term risks of ultrasound, if any, are unknown, but there are many benefits." (ACOG) Others warn that it is insufficiently tested, and make comparisons with X-rays and DES, which were once considered safe. The main area of debate is whether ultrasound is being used too frequently in a routine fashion in healthy pregnancies, without thorough enough testing. There may be some association between ultrasound and low birth weight (Blatt). (Altho' this is difficult to prove because the opposite assertion is known to be true: i.e. if there is IUGR (intra-uterine growth retardation) US will be performed more regularly to assess the progress of the baby.) Some people express concern about the heat and cavitation (bubbling in the cells). Others wonder whether routine ultrasound is cost effective, or whether the money involved would be more effectively spent elsewhere. A Consensus Development Conference of the National Institutes of Health (NIH) was convened to consider the use of ultrasound in pregnancy, and concluded that "Diagnostic ultrasound is considered to be a low-risk procedure. However, routine use of ultrasound in pregnancy should be discouraged." (Blatt) They recommended ultrasound only for twenty-eight specific instances. (The use of diagnostic ultrasound in pregnancy. Washington, DC. Government Printing Office, 1984.) In contrast, Germany, France, and the UK have adopted a policy of ultrasound for all pregnancies. (NEJM, 1/14/93, Prenatal Diagnosis) ----------------------------------------- From Robbrenner@aol.com (Robert Brenner MD): The theoretical risk of fetal exposure to sound waves has never been shown to cause any fetal damage. The biggest risk of ultrasound is overinterpretation or missed diagnosis. ----------------------------------------- From: samador@haverford.edu (Suzanne Amador) Suggested addition to the Ultrasound FAQ section on Ultrasound Safety: Here are a list of references from the medical literature on human population studies which examine the risks and benefits of ultrasound screening during pregnancy. These references show that there is presently very good evidence that no short or long-term effects result from prenatal exposure to ultrasound. However, ultrasound exposure at high intensities and long exposure times can cause problems in laboratory animals. (see refs. (1, 2), for example.) Most of these problems appear to be due to the heating which can result from long, high intensity ultrasound. Thus, these human population studies have been conducted to see whether such effects occur at the exposure times and intensities actually used in clinical prenatal ultrasound. None of the studies listed below specifically address vaginal ultrasound exams or long-term exposure to Doppler ultrasound. Several large human population studies have been performed in which thousands to tens of thousands of women in low-risk pregnancies are assigned randomly to either control groups or routinely-exposed groups. The control groups are assigned to receive no routine ultrasound exams, while the routinely-exposed groups are routinely examined, regardless of need. Women in either group are given ultrasound exams if a problem arises which makes the exam medically necessary, but no women are moved between groups after their initial assignments. (This ensures that women who develop problems during pregnancy aren't steadily moved from the control to the routinely-exposed group. Were this the case, it would not be surprising that the incidence of problems would increase in the routinely-exposed group.) All but one of the large studies show no evidence of harm, even for the large populations studied. (see refs (4, 7) and references therein.) The study by Newnham et al. (ref. 6) did see an increase in the percentage of low-birthweight babies in an intensively-examined group versus a control group receiving a very low average number of exams; apart from this difference, the two groups had identical pregnancy outcomes. However, similarly conducted studies (refs. 4, 7) examined much larger populations, and found no problems. Newnham also notes that the average difference in birthweights between the two groups was very small, so that the finding could have been an accident due to small numbers of cases. Some studies don't bear out advantages from routine ultrasound for low-risk pregnancies (see refs. 4,6). These studies are always designed to exclude women who already have indications that their pregnancies will present problems, such as unexplained bleeding, the assumption being that ultrasound exams offer a net benefit for pregnancies with known risk factors. However, some physicians think that these studies underestimate the benefits of routine ultrasound; objections such as these are aired in the correspondence following (refs. 4 and 6). Most of the population studies listed below only follow women through pregnancy and birth, but some are of long enough term to study children past infancy (refs. 5,8,9) These are again reassuring, although the numbers of children followed is much smaller than in the studies of infants immediately after birth. One study (ref. 3) received wide media coverage because it purported to show an association between hearing loss and ultrasound exams. The authors studied a condition, delayed speech, in a group of Canadian children. This condition is not known to be caused by physiological problems, and may be a problem with psychological origins. In their study, they compared a group of children with this condition with a group of children of the same size without delayed speech. This matching of the two groups was performed after the fact, rather than by following two groups of children from birth and watching them potentially develop this problem. The numbers of children studied were very small (under one hundred, compared to the much larger numbers examined in every other study mentioned here), and the researchers didn't control for numerous other factors. Other major problems in this study are detailed in the correspondence following the article, in which the authors actually state that they do not consider their work to show a link between ultrasound and delayed speech. References on obstetrical diagnostic ultrasound and studies of ultrasound safety: 1. Barnett, G.R. ter Haar, M.C. Ziskin, W.L. Nyborg, K. Maeda, J. Bang, "Current status of research on biophysical effects of ultrasound," Ultrasound in Medicine and Biology, vol. 20 (1994) pp. 205-218. 2. Bioeffects and Safety of Diagnostic Ultrasound, American Institute of Ultrasound in Medicine, Rockville, Maryland, 1993. 3. Campbell, R.W. Elford, R.F. Brant, "Case-control study of prenatal ultrasonography exposure in children with delayed speech," Canadian Medical Association Journal, vol. 149 (Nov. 15, 1993), pp. 1435-40; Also read the related correspondence in the same journal, vol. 150 (March 1, 1994), pp. 647-9. 4. Ewigman, J.P. Crane, F.D. Frigoletto, "Effect of Prenatal Ultrasound Screening on perinatal outcome," New England Journal of Medicine, Vol. 329, pp. 821-7, 1993. 5. Lyons, C. Dyke, and M. Toms, "In utero exposure to diagnostic ultrasound: a six year followup," Radiology, vol. 166 (1988) pp. 687-690. 6. Newnham, John P., Sharon F. Evans, Con A. Michael, Fiona J. Stanley, and Louis I. Landau, "Effects of frequent ultrasound during pregnancy: a randomised controlled trial," The Lancet, Vol. 342, October 9, 1993, pp. 887-891; see also related correspondence in the same journal, Nov. 27, 1993, pp. 1359-61 and Jan. 15, 1994, p. 178. 7. Saarri-Kemppainen, O. Karjalainen, P. Ylostalo, O.P. Heinonen, "Ultrasound screening and perinatal mortality: controlled trial of systematic one-stage screening in pregnancy. The Helsinki Ultrasound Trial," The Lancet, vol. 336 (1990), pp. 387- 391. 8. Scheidt, F. Stanley, D.A. Bryla, "One year follow-up of infants exposed to ultrasound in utero," American Journal of Obstetrics and Gynecology, vol. 131 (1978), pp. 743- 748. 9. Stark, M. Orleans, A.D. Havercamp, "Short and long-term risks after exposure to diagnostic ultrasound in utero." Obstetrics and Gynecology, vol. 63 (1984) pp. 194- 200. ----------------------------------------- 5. Do you really have to have a full bladder for an ultrasound? Women getting an ultrasound are encouraged to drink several glasses of water an hour before the exam and not go to the bathroom until after the exam. The full bladder helps the doctor locate the pelvic organs and get a clearer and more accurate picture. However, this advice only applies for some ultrasounds, depending on the kind of probe used and the point in pregnancy when the ultrasound is done. This is why different women report getting different advice from their doctors about whether a full bladder is required. ----------------------------------------- From Robbrenner@aol.com (Robert Brenner MD): The two types of ultrasound are abdominal and vaginal ultrasound. Vaginal ultrasound is the most accurate up to 12 weeks gestation and does not require a full bladder. Abdominal ultrasound requires a full bladder up to about 14-16 weeks. ----------------------------------------- Sources: The American College of Obstetricians and Gynecologists (abbreviated in references as ACOG). Planning for Pregnancy, Birth, and Beyond. A Dutton Book, May, 1992. Blatt, Robin J.R. Prenatal Tests. Vintage Books. New York, August 1988. The Boston Women's Health Collective. The New Our Bodies, Our Selves. Simon and Schuster. New York, NY, 1992. Rothman, Barbara Katz. The Tentative Pregnancy. Viking Penguin Inc. New York, NY, 1986. Scher, Jonathan, M.D., and Dix, Carol. Will My Baby Be Normal? How to Make Sure. The Dial Press. New York. 1983. Lynn Gazis-Sax