The American College of Radiology, with more than 30,000 members, is the principal organization of radiologists, radiation oncologists, and clinical medical physicists in the United States. The College is a nonprofit professional society whose primary purposes are to advance the science of radiology, improve radiologic services to the patient, study the socioeconomic aspects of the practice of radiology, and encourage continuing education for radiologists, radiation oncologists, medical physicists, and persons practicing in allied professional fields. The American College of Radiology will periodically define new practice guidelines and technical standards for radiologic practice to help advance the science of radiology and to improve the quality of service to patients throughout the United States. Existing practice guidelines and technical standards will be reviewed for revision or renewal, as appropriate, on their fifth anniversary or sooner, if indicated. Each practice guideline and technical standard, representing a policy statement by the College, has undergone a thorough consensus process in which it has been subjected to extensive review, requiring the approval of the Commission on Quality and Safety as well as the ACR Board of Chancellors, the ACR Council Steering Committee, and the ACR Council. The practice guidelines and technical standards recognize that the safe and effective use of diagnostic and therapeutic radiology requires specific training, skills, and techniques, as described in each document. Reproduction or modification of the published practice guideline and technical standard by those entities not providing these services is not authorized.

Revised 2007 (Res. 25)*

ACR–ACOG–AIUM PRACTICE GUIDELINE FOR THE PERFORMANCE OF OBSTETRICAL

PREAMBLE

These guidelines are an educational tool designed to assist Therefore, it should be recognized that adherence to these practitioners in providing appropriate radiologic care for guidelines will not assure an accurate diagnosis or a patients. They are not inflexible rules or requirements of successful outcome. All that should be expected is that the practice and are not intended, nor should they be used, to practitioner will follow a reasonable course of action establish a legal standard of care. For these reasons and based on current knowledge, available resources, and the those set forth below, the American College of Radiology needs of the patient to deliver effective and safe medical cautions against the use of these guidelines in litigation in care. The sole purpose of these guidelines is to assist which the clinical decisions of a practitioner are called practitioners in achieving this objective. into question. I. INTRODUCTION The ultimate judgment regarding the propriety of any specific procedure or course of action must be made by The clinical aspects contained in specific sections of this the physician or medical physicist in light of all the guideline (Introduction, Classification of Fetal circumstances presented. Thus, an approach that differs Sonographic Examinations, Specifications of the from the guidelines, standing alone, does not necessarily Examination, Equipment Specifications, and Fetal Safety) imply that the approach was below the standard of care. were revised collaboratively by the American College of To the contrary, a conscientious practitioner may Radiology (ACR), the American Institute of Ultrasound in responsibly adopt a course of action different from that Medicine (AIUM), and the American College of set forth in the guidelines when, in the reasonable Obstetricians and Gynecologists (ACOG). Recom- judgment of the practitioner, such course of action is mendations for physician qualifications, written request indicated by the condition of the patient, limitations of for the examination, procedure documentation, and available resources, or advances in knowledge or quality control vary among the three organizations and are technology subsequent to publication of the guidelines. addressed by each separately. However, a practitioner who employs an approach substantially different from these guidelines is advised to This guideline has been developed for use by practitioners document in the patient record information sufficient to performing obstetrical sonographic studies. Fetal explain the approach taken. ultrasound1 should be performed only when there is a valid medical reason, and the lowest possible ultrasonic The practice of medicine involves not only the science, exposure settings should be used to gain the necessary but also the art of dealing with the prevention, diagnosis, diagnostic information. A limited examination may be alleviation, and treatment of disease. The variety and performed in clinical emergencies or for a limited purpose complexity of human conditions make it impossible to such as evaluation of fetal or embryonic cardiac activity, always reach the most appropriate diagnosis or to predict with certainty a particular response to treatment. 1The consensus of the committee was that the use of the terms “ultrasound” or “sonography” is at the discretion of each organization.

PRACTICE GUIDELINE Obstetrical Ultrasound / 1 fetal , or volume. A limited follow- IV. WRITTEN REQUEST FOR THE up examination may be appropriate for re-evaluation of EXAMINATION fetal size or interval growth or to re-evaluate abnormalities previously noted if a complete prior The written or electronic request for an obstetrical examination is on record. ultrasound examination should provide sufficient information to demonstrate the medical necessity of the While this guideline describes the key elements of examination and allow for its proper performance and standard sonographic examinations in the first trimester interpretation. and second and third trimesters, a more detailed anatomic examination of the may be necessary in some cases, Documentation that satisfies medical necessity includes 1) such as when an abnormality is found or suspected on the signs and symptoms and/or 2) relevant history (including standard examination or in at high risk for known diagnoses). Additional information regarding the fetal anomalies. In some cases, other specialized specific reason for the examination or a provisional examinations may be necessary as well. diagnosis would be helpful and may at times be needed to allow for the proper performance and interpretation of the While it is not possible to detect all structural congenital examination. anomalies with diagnostic ultrasound, adherence to the following guidelines will maximize the possibility of The request for the examination must be originated by a detecting many fetal abnormalities. physician or other appropriately licensed health care provider. The accompanying clinical information should II. CLASSIFICATION OF FETAL be provided by a physician or other appropriately licensed SONOGRAPHIC EXAMINATIONS health care provider familiar with the patient’s clinical problem or question and consistent with the state’s scope A. First Trimester Ultrasound Examination of practice requirements. (ACR Resolution 35, adopted in 2006) B. Standard Second or Third Trimester Examination V. SPECIFICATIONS OF THE A standard obstetrical sonogram in the second or third EXAMINATION trimester includes an evaluation of fetal presentation, amniotic fluid volume, cardiac activity, placental position, A. First Trimester Ultrasound Examination fetal biometry, and fetal number, plus an anatomic survey. The maternal cervix and adnexa should be examined as 1. Indications clinically appropriate when technically feasible. A sonographic examination can be of benefit in C. Limited Examination many circumstances in the first trimester2 of , including, but not limited to, the A limited examination is performed when a specific following indications: question requires investigation. For example, a limited a. To confirm the presence of an intrauterine examination could be performed to confirm fetal heart pregnancy. activity in a bleeding patient or to verify fetal presentation b To evaluate a suspected ectopic pregnancy. in a laboring patient. In most cases limited sonographic c. To define the cause of vaginal bleeding. examinations are appropriate only when a prior complete d. To evaluate pelvic pain. examination is on record. e. To estimate gestational (menstrual3) age. f. To diagnose or evaluate multiple gestations. D. Specialized Examinations g. To confirm cardiac activity. h. As an adjunct to chorionic villus sampling, A detailed anatomic examination is performed when an embryo transfer, and localization and anomaly is suspected on the basis of history, biochemical removal of an intrauterine device (IUD). abnormalities, or the results of either the limited or i. To assess for certain fetal anomalies, such as standard scan. Other specialized examinations might anenecephaly, in high risk patients. include fetal Doppler, , fetal j. To evaluate maternal pelvic masses and/or echocardiogram, or additional biometric measurements. uterine abnormalities.

III. QUALIFICATIONS AND RESPONSIBILITIES OF PERSONNEL 2For the purpose of this document, first trimester represents 1w-

13w + 6d. See the ACR Practice Guideline for Performing and 3 Interpreting Diagnostic Ultrasound Examinations. For the purpose of this document, the terms “gestational” and “menstrual” age are considered equivalent.

2 / Obstetrical Ultrasound PRACTICE GUIDELINE k. To measure the nuchal translucency (NT) c. Fetal number should be reported. when part of a screening program for fetal . Comment l. To evaluate suspected hydatidiform mole. Amnionicity and chorionicity should be documented for all multiple gestations when Comment possible. Limited examination may be performed to evaluate interval growth, estimate amniotic fluid d. Embryonic/fetal anatomy appropriate for the volume, evaluate the cervix, and assess the first trimester should be assessed. presence of cardiac activity. e. The uterus including the cervix, adnexal 2. Imaging parameters structures, and cul-de-sac should be evaluated. Comment Scanning in the first trimester may be performed Comment either transabdominally or transvaginally. If a The presence, location, and size of adnexal transabdominal examination is not definitive, a masses should be recorded. The presence of transvaginal scan or transperineal scan should be leiomyomata should be recorded, and performed whenever possible. measurements of the largest or any potentially clinically significant leio- a. The uterus, including the cervix, and adnexa myomata may be recorded. The cul-de-sac should be evaluated for the presence of a should be evaluated for the presence or gestational sac. If a gestational sac is seen, absence of fluid. its location should be documented. The gestational sac should be evaluated for the f. If possible, the appearance of the nuchal presence or absence of a yolk sac or embryo, region should be assessed as part of a first and the crown-rump length should be trimester scan where a live fetus is present. recorded, when possible. Comment Comment For those patients desiring to assess their The crown-rump length is a more accurate individual risk of fetal aneuploidy, a very indicator of gestational (menstrual) age than specific measurement of the NT during a is mean gestational sac diameter. However, specific age interval is necessary (as the mean gestational sac diameter may be determined by the laboratory used). See the recorded when an embryo is not identified. guidelines for this measurement below.

Caution should be used in making the NT measurements should be used (in presumptive diagnosis of a gestational sac in conjunction with serum biochemistry) to the absence of a definite embryo or yolk sac. determine the risk for having a child with Without these findings an intrauterine fluid , trisomy 13, trisomy 18, or collection could represent a pseudo- other anatomical abnormalities such as heart gestational sac associated with an ectopic defects. In this setting, it is important that pregnancy. the practitioner measure the NT according to established guidelines for measurement. A b. Presence or absence of cardiac activity quality assessment program is recommended should be reported. to ensure that false-positive and false- negative results are kept to a minimum. Comment With transvaginal scans, cardiac motion is Guidelines for NT measurement: usually observed when the embryo is 5 mm or greater in length. If an embryo less than 5 i. The margins of the NT edges must be mm in length is seen without cardiac clear enough for proper placement of activity, a subsequent scan at a later time the calipers. may be needed to assess the presence or ii. The fetus must be in the midsagittal absence of cardiac activity. plane.

PRACTICE GUIDELINE Obstetrical Ultrasound / 3 iii. The image must be magnified so that it vii. Electronic calipers must be placed on is filled by the fetal head, neck, and the inner borders of the nuchal space upper thorax. with none of the horizontal crossbar iv. The fetal neck must be in a neutral itself protruding into the space. position – not flexed and not hyper- viii. The calipers must be placed extended. perpendicular to the long axis of the v. The amnion must be seen as separate fetus. from the NT line. ix. The measurement must be obtained at vi. The (+) calipers on the ultrasound must the widest space of the NT. be used to perform the NT measurement.

Diagram for the nuchal translucency measurement.

4 / Obstetrical Ultrasound PRACTICE GUIDELINE B. Second and Third Trimester Ultrasound Examination chorionicity, amnionicity, comparison of fetal sizes, estimation of amniotic fluid 1. Indications volume (increased, decreased, or normal) on each side of the membrane, and fetal Ultrasound can be of benefit in many situations genitalia (when visualized). in the second and third trimester, including, but not limited to, the following circumstances: b. A qualitative or semiquantitative estimate of (adapted from NIH publication 84-667, 1984) amniotic fluid volume should be reported. a. Estimation of gestational (menstrual) age. b. Evaluation of fetal growth. Comment c. Vaginal bleeding. Although it is acceptable for experienced d. Abdominal or pelvic pain. examiners to qualitatively estimate amniotic e. Cervical insufficiency. fluid volume, semi-quantitative methods f. Determination of fetal presentation. have also been described for this purpose g. Suspected multiple gestation. (e.g., , single deepest h. Adjunct to or other pocket, two-diameter pocket). procedure. i. Significant discrepancy between uterine size c. The placental location, appearance, and and clinical dates. relationship to the internal cervical os should j. Pelvic mass. be recorded. The umbilical cord should be k. Suspected hydatidiform mole. imaged, and the number of vessels in the l. Adjunct to cervical cerclage placement. cord should be evaluated when possible. m. Suspected ectopic pregnancy. n. Suspected fetal death. Comment o. Suspected uterine abnormality. It is recognized that apparent placental p. Evaluation of fetal well-being. position early in pregnancy may not q. Suspected amniotic fluid abnormalities. correlate well with its location at the time of r. Suspected placental abruption. delivery. s. Adjunct to external cephalic version. t. Premature and/or Transabdominal, transperineal, or trans- premature labor. vaginal views may be helpful in visualizing u. Abnormal biochemical markers. the internal cervical os and its relationship to v. Follow-up evaluation of a fetal anomaly. the . w. Follow-up evaluation of placental location for suspected placenta previa. Transvaginal or transperineal ultrasound x. History of previous congenital anomaly. may be considered if the cervix appears y. Evaluation of fetal condition in late shortened or cannot be adequately visualized registrants for . during the transabdominal sonogram. z. To assess for findings that may increase the risk for aneuploidy. d. Gestational (menstrual) age assessment aa. Screening for fetal anomalies. First-trimester crown-rump measurement is Comment the most accurate means for sonographic In certain clinical circumstances, a more detailed dating of pregnancy. Beyond this period, a examination of fetal anatomy may be indicated. variety of sonographic parameters such as biparietal diameter, abdominal circum- 2. Imaging parameters for a standard fetal ference, and femoral diaphysis length can be examination used to estimate gestational (menstrual) age. a. Fetal cardiac activity, fetal number, and The variability of gestational (menstrual) presentation should be reported. age estimations, however, increases with advancing pregnancy. Significant discre- Comment pancies between gestational (menstrual) age Abnormal heart rate and/or rhythm should and fetal measurements may suggest the be reported. possibility of fetal growth abnormality, intrauterine growth restriction, or Multiple gestations require the macrosomia. documentation of additional information:

PRACTICE GUIDELINE Obstetrical Ultrasound / 5 Comment Comment The pregnancy should not be redated after If previous studies have been performed, an accurate earlier scan has been performed appropriateness of growth should also be and is available for comparison. reported. Scans for growth evaluation can i. Biparietal diameter is measured at the typically be performed at least 2 to 4 weeks level of the thalami and cavum septi apart. A shorter scan interval may result in pellucidi. The cerebellar hemispheres confusion as to whether anatomic changes should not be visible in this scanning are truly due to growth as opposed to plane. The measurement is taken from variations in the measurement technique the outer edge of the proximal skull to itself. the inner edge of the distal skull. Currently, even the best fetal weight Comment prediction methods can yield errors as high The head shape may be flattened as ±15 percent. This variability can be (dolichocephaly) or rounded influenced by factors such as the nature of (brachycephaly) as a normal variant. the patient population, the number and types Under these circumstances, certain of anatomic parameters being measured, variants of normal fetal head develop- technical factors that affect the resolution of ment may make measurement of the ultrasound images, and the weight range head circumference more reliable than being studied. biparietal diameter for estimating gestational (menstrual) age. f. Maternal anatomy ii. Head circumference is measured at the Evaluation of the uterus, adnexal structures, same level as the biparietal diameter, and cervix should be performed when around the outer perimeter of the appropriate. If the cervix cannot be calvarium. This measurement is not visualized, a transperineal or transvaginal affected by head shape. scan may be considered when evaluation of iii. Femoral diaphysis length can be the cervix is needed. reliably used after 14 weeks gestational (menstrual) age. The long axis of the Comment femoral shaft is most accurately This will allow recognition of incidental measured with the beam of insonation findings of potential clinical significance. being perpendicular to the shaft, The presence, location, and size of adnexal excluding the distal femoral epiphysis. masses and the presence of at least the iv. Abdominal circumference or average largest and potentially clinically significant abdominal diameter should be leiomyomata may be recorded. It is determined at the skin line on a true frequently not possible to image the normal transverse view at the level of the maternal ovaries during the second and third junction of the umbilical vein, portal trimesters. sinus, and fetal stomach when visible. g. Fetal anatomic survey Comment Fetal anatomy, as described in this Abdominal circumference or average document, may be adequately assessed by abdominal diameter measurement is ultrasound after approximately 18 weeks used with other biometric parameters to gestational (menstrual) age. It may be estimate fetal weight and may allow possible to document normal structures detection of intrauterine growth before this time, although some structures restriction or macrosomia. can be difficult to visualize due to fetal size, position, movement, abdominal scars, and e. Fetal weight estimation increased maternal abdominal wall Fetal weight can be estimated by obtaining thickness. A second or third trimester scan measurements such as the biparietal may pose technical limitations for an diameter, head circumference, abdominal anatomic evaluation due to imaging artifacts circumference or average abdominal from acoustic shadowing. When this occurs, diameter, and femoral diaphysis length. the report of the sonographic examination Results from various prediction models can should document the nature of this technical be compared to fetal weight percentiles from limitation. A follow-up examination may be published nomograms. helpful.

6 / Obstetrical Ultrasound PRACTICE GUIDELINE The following areas of assessment represent and image orientation. An official interpretation (final the minimal elements of a standard report) of the ultrasound examination should be included examination of fetal anatomy. A more in the patient’s medical record. Retention of the detailed fetal anatomic examination may be ultrasound examination images should be consistent both necessary if an abnormality or suspected with clinical need and with relevant legal and local abnormality is found on the standard healthcare facility requirements. examination. i. Head, face, and neck Reporting should be in accordance with the ACR Practice Cerebellum Guideline for Communication of Diagnostic Imaging Choroid plexus Findings. Cisterna magna Lateral cerebral ventricles VII. EQUIPMENT SPECIFICATIONS Midline falx Cavum septum pellucidum These studies should be conducted with real-time Upper lip scanners, using a transabdominal and/or transvaginal approach. A transducer of appropriate frequency should Comment be used. A measurement of the nuchal fold may be helpful during a specific age interval to Comment suggest an increased risk of aneuploidy. Real time sonography is necessary to confirm the ii. Chest presence of fetal life through observation of cardiac The basic cardiac examination activity and active movement. includes a four-chamber view of the fetal heart. The choice of transducer frequency is a trade-off between beam penetration and resolution. With modern equipment, If technically feasible, views of the 3 to 5 MHz abdominal transducers allow sufficient outflow tracts should be attempted as penetration in most patients while providing adequate part of the cardiac screening resolution. A lower-frequency transducer (2 to 2.25 MHz) examination. may be needed to provide adequate penetration for iii. Abdomen abdominal imaging in an obese patient. During early Stomach (presence, size, and situs) pregnancy, a 5 MHz abdominal transducer or a 5 to 10 Kidneys MHz or greater vaginal transducer may provide superior Bladder resolution while still allowing adequate penetration. Umbilical cord insertion site into the fetal abdomen VIII. FETAL SAFETY Umbilical cord vessel number iv. Spine Diagnostic ultrasound studies of the fetus are generally Cervical, thoracic, lumbar, and sacral considered to be safe during pregnancy. This diagnostic spine procedure should be performed only when there is a valid v. Extremities medical indication, and the lowest possible ultrasonic Legs and arms – presence or absence exposure setting should be used to gain the necessary vi. Gender diagnostic information under the “as low as reasonably Medically indicated in low-risk achievable” (ALARA) principle. pregnancies only for evaluation of multiple gestations. The promotion, selling, or leasing of ultrasound equipment for making “keepsake fetal videos” is VI. DOCUMENTATION considered by the U.S. Food and Drug Administration to be an unapproved use of a medical device [9]. Use of a Adequate documentation of the study is essential for high- diagnostic ultrasound system for these purposes, without a quality patient care. There should be a permanent record physician’s order, may be in violation of state laws or of the ultrasound examination and its interpretation. regulations. Comparison with prior relevant imaging studies may prove helpful. Images of all appropriate areas, both normal and abnormal, should be recorded. Variations from normal size should generally be accompanied by measurements. Images should be labeled with the patient identification, facility identification, examination date,

PRACTICE GUIDELINE Obstetrical Ultrasound / 7 IX. QUALITY CONTROL AND Ruth B. Goldstein, MD IMPROVEMENT, SAFETY, INFECTION Beatrice L. Madrazo, MD CONTROL, AND PATIENT EDUCATION Jon W. Meilstrup, MD Michelle L. Melany, MD All probes should be cleaned after use. Vaginal probes Miriam N. Mikhail, MD should be covered by a protective sheath prior to Sara M. O’Hara, MD insertion. Following the examination, the sheath should Suhas G. Parulekar, MD be disposed of and the probe cleaned in an antimicrobial John S. Pellerito, MD solution. The type of solution and amount of time for Philip W. Ralls, MD cleaning depend on manufacturer and infectious disease Michelle L. Robbin, MD recommendations. Carol M. Rumack, MD, Chair, Commission

Policies and procedures related to quality, patient Comments Reconciliation Committee education, infection control, and safety should be Marcela Bohm-Velez, MD, Co-Chair developed and implemented in accordance with the ACR Bill H. Warren, MD, Co-Chair Policy on Quality Control and Improvement, Safety, Beryl R. Benacerraf, MD Infection Control, and Patient Education appearing under Carol B. Benson, MD the heading Position Statement on QC & Improvement, Douglas L. Brown, MD Safety, Infection Control, and Patient Education on the Harris J. Finberg, MD ACR web page (http://www.acr.org/guidelines). Mary C. Frates, MD Ruth B. Goldstein, MD Equipment performance monitoring should be in Gretchen A. Gooding, MD accordance with the ACR Technical Standard for Gail C. Hansen, MD Diagnostic Medical Physics Performance Monitoring of Paul A. Larson, MD Real Time Ultrasound Equipment. Lawrence A. Liebscher, MD Carol M. Rumack, MD ACKNOWLEDGEMENTS Julie K. Timins, MD William G. Way, Jr., MD This guideline was revised according to the process described under the heading The Process for Developing Suggested Reading (Additional articles that are not cited ACR Practice Guidelines and Technical Standards on the in the document but that the committee recommends for ACR web page (http://www.acr.org/guidelines) by the further reading on this topic) ACR Guidelines and Standards Committee of the Commission on Ultrasound in collaboration with the 1. Altman DG, Chitty LS. New charts for ultrasound AIUM and the ACOG. dating of pregnancy. Ultrasound Obstet Gynecol 1997;10:174-191. Principal Reviewer: Beryl R. Benacerraf, MD 2. Barnett SB, Ter Haar GR, Ziskin MC, Rott HD, Duck FA, Maeda K. International recommendations and Collaborative Subcommittee guidelines for the safe use of diagnostic ultrasound in medicine. Ultrasound Med Biol 2000;26:355-366. ACR 3. Benacerraf B. The significance of the nuchal fold in Beryl R. Benacerraf, MD, Chair the second trimester fetus. Prenat Diagn 2002; Ruth B. Goldstein, MD 22:798-801. 4. Bly S, Van den Hof MC, Diagnostic Imaging AIUM Committee, Society of Obstetricians and Harris Finburg, MD Gynaecologists of Canada. Obstetric ultrasound Wesley Lee, MD biological effects and safety. J Obstet Gynaecol Can Larry Platt, MD 2005;27:572-580. 5. Bulas DI, Fonda JS. Prenatal evaluation of fetal ACOG anomalies. Pediatr Clin North Am 1997;44:537-553. 6. Callen PW. The obstetric ultrasound examination. In: Fredric Frigoletto, Jr., MD Ultrasonography in and Gynecology 4th William N.P. Herbert, MD edition. Philadelphia, Pa: WB Saunders; 2000:1-17. Carolyn M. Zelop, MD 7. Chambers SE, Muir BB, Haddad NG. Ultrasound

evaluation of ectopic pregnancy including correlation ACR Guidelines and Standards Committee with human chorionic gonadotropin levels. Br J Gretchen A. Gooding, MD, Chair Radiol 1990;63:246-250. Raymond E. Bertino, MD Mary C. Frates, MD

8 / Obstetrical Ultrasound PRACTICE GUIDELINE 8. Deter RL, Harrist RB. Growth standards for anatomic 23. Maymon R, Shulman A, Ariely S, Halperin R, Caspi measurements and growth rates derived from E, Weinraub Z. Sonographic assessment of cervical longitudinal studies of normal fetal growth. J Clin changes during pregnancy and delivery: current Ultrasound 1992;20:381-388. concepts. Eur J Obstet Gynecol Reprod Biol 9. Food and Drug Administration. Fetal Keepsake 1996;67:149-155. Video, September 2002. Available at: 24. Miller MW, Brayman AA, Abramowicz JS. Obstetric http://www.fda.gov/cdrh/consumer/fetalvideos.html. ultrasonography: a biophysical consideration of Accessed March 1, 2006. patient safety – the “rules” have changed. Am J 10. Garmel SH, D’Alton ME. Diagnostic ultrasound in Obstet Gynecol 1998;179:241-254. pregnancy: an overview. Semin Perinatol 25. Owen P, Donnet ML, Ogston SA, Christie AD, 1994;18:117-132. Howie PW, Patel NB. Standards for ultrasound fetal 11. Hadlock FP, Harrist RB, Carpenter RJ, Deter RL, growth velocity. Br J Obstet Gynecol 1996;103:60- Park SK. Sonographic estimation of fetal weight: the 69. value of femur length in addition to head and 26. Prenatal Diagnosis of Fetal Chromosomal abdomen measurements. Radiology 1984;150:535- Abnormalities. District of Columbia: American 540. College of Obstetricians and Gynecologists; ACOG 12. Hadlock FP, Harrist RB, Sharman RS, Deter RL, Practice Bulletin; Number 27; 2001. Park SK. Estimation of fetal weight with the use of 27. Seeds JW. The routine or screening obstetrical head, body, and femur measurements: a prospective ultrasound examination. Clin Obstet Gynecol study. Am J Obstet Gynecol 1985;151:333-337. 1996;39:814-830. 13. Harris RD, Cho C, Wells WA. Sonography of the 28. Sheiner E, Freeman J, Abramowicz JS. Acoustic placenta with emphasis on pathological correlation. output as measured by mechanical and thermal Semin Ultrasound CT MR 1996;17:66-89. indices during routine obstetric ultrasound 14. Hill LM, Kislak S, Martin JG. Transvaginal examinations. J Ultrasound Med 2005;24:1665-1670. sonographic detection of the pseudogestational sac 29. Smith-Bindman R, Hosmer W, Feldstein VA, Deeks associated with ectopic pregnancy. Obstet Gynecol JJ, Goldberg JD. Second-trimester ultrasound to 1990;75:986-988. detect with Down syndrome: a meta-analysis. 15. International Society of Ultrasound in Obstetrics and JAMA 2001;285:1044-1055. Gynecology. Cardiac screening examination of the 30. Snijders RJ, Noble P, Sebire N, Souka A, Nicolaides fetus: guidelines for performing the “basic” and KH. UK multicentre project on assessment of risk of “extended basic” cardiac scan. Ultrasound Obstet trisomy 21 by maternal age and fetal nuchal- Gynecol 2006;27:107-13. translucency thickness at 10-14 weeks of gestation. 16. Kirk JS, Comstock CH, Lee W, Smith RS, Riggs Fetal Medicine Foundation First Trimester Screening TW, Weinhouse E. Sonographic screening to detect Group. Lancet 1998;352:343-346. fetal cardiac anomalies: a 5-year experience with 111 31. Wapner R, Thom E, Simpson JL, et al. First abnormal cases. Obstet Gynecol 1997;89:227-232. Trimester Maternal Serum Biochemistry and Fetal 17. Laing FC, Frates MC. Ultrasound evaluation during Nuchal Translucency Screening (BUN) Study Group. the first trimester of pregnancy. In: Ultrasonography First-trimester screening for trisomies 21 and 18. N in Obstetrics and Gynecology. 4th edition. Engl J Med 2003;349:1405-1413. Philadelphia, Pa: WB Saunders; 2000:105-145. 18. Lee W. Performance of the basic fetal cardiac *Guidelines and standards are published annually with an ultrasound examination. J Ultrasound Med effective date of October 1 in the year in which amended, 1998;17:601-607. Erratum in J Ultrasound Med revised or approved by the ACR Council. For guidelines 1998;17:796. and standards published before 1999, the effective date 19. Magann EF, Sanderson M, Martin JN, Chauhan S. was January 1 following the year in which the guideline The amniotic fluid index, single deepest pocket, and or standard was amended, revised, or approved by the two-diameter pocket in normal human pregnancy. Am ACR Council. J Obstet Gynecol 2000;182:1581-1588. 20. Mahony BS. Ultrasound of the cervix during Development Chronology for this Guideline pregnancy. Abdom Imaging 1997;22:569-578. 1990 (Resolution 5) 21. Malone FD, Canick JA, Ball RH, et al. First-trimester Revised 1995 (Resolution 35) or second-trimester screening, or both, for Down’s Revised 1999 (Resolution 37) syndrome. N Engl J Med 2005;353:2001-2011. Revised 2003 (Resolution 19) 22. Marinac-Dabic D, Krulewitch CJ, Moore RM Jr. The Amended 2006 (Resolution 35) safety of prenatal ultrasound exposure in human Revised 2007 (Resolution 25) studies. Epidemiology 2002;13:S19-S22.

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