Nuchal Translucency Measurement on the Fetus in a Difficult Position

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298jum_online.qxp:Layout 1 7/20/10 10:35 AM Page 1261Tips and TechniquesTricks for Obtaining a NuchalTranslucency Measurement on theFetus in a Difficult PositionBryann Bromley, MD, Thomas D. Shipp, MD, Mary Ann Mitchell, RDMS, Beryl R. Benacerraf, MDcreening for aneuploidy should be offered to allpregnant women.1 The demand for first-trimestersonography has been increasing rapidly as manySwomen choose first-trimester risk assessmentthat involves the sonographic measurement of the fetalnuchal translucency (NT). Although most studies are eas-ily accomplished using a standard transabdominalapproach within a 20-minute window, not infrequently,the fetus may be positioned such that an adequate mea-surement of the NT is not possible. For example, Wax etal2 reported that they were able to obtain an NT mea-Abbreviationssurement in only 80% of eligible women at the time of theNT, nuchal translucencyfirst visit, despite allowing up to 30 to 40 minutes beforeabandoning the examination. Repeat scanning of thepatients who returned resulted in an 86.6% success rate.2The fetal position was consistently a factor in not beingable to obtain an NT measurement, accounting for 67.3%of such cases.2 Other factors that prevent optimal mea-Received February 23, 2010, from the Departments ofRadiology and Obstetrics and Gynecology, Brighamsurement of the NT include a high maternal body massand Women’s Hospital (B.B., T.D.S., B.R.B.), andindex, as imaging in these patients generally requiresDepartments of Radiology (B.R.B.) and Obstetrics andGynecology (B.B., B.R.B.), Massachusetts Generalmore time and more return visits, ultimately resulting inHospital, Harvard Medical School, Boston,a higher failure rate.3Massachusetts USA; and Diagnostic UltrasoundWe have developed 2 scanning techniques thatAssociates, PC, Boston, Massachusetts USA (B.B.,T.D.S., M.A.M., B.R.B.). Revision requested March 15,enhance the chances that an adequate NT measurement2010. Revised manuscript accepted for publicationwill be obtained within the 20-minute time window.March 17, 2010.Guest Editor: Alfred Z. Abuhamad, MD.These techniques are based on approaching the uterusAddress correspondence to Bryann Bromley,(and fetus) at right angles from the initial orientation,MD, Diagnostic Ultrasound Associates, PC, 333thus increasing the chances that the fetus will be imagedLongwood Ave, Suite 400, Boston, MA 02115 USA.E-mail: [email protected] the midsagittal view.© 2010 by the American Institute of Ultrasound in Medicine • J Ultrasound Med 2010; 29:1261–1264 • 0278-4297/10/$3.50298jum_online.qxp:Layout 1 7/20/10 10:35 AM Page 1262Nuchal Translucency Measurement on the Fetus in a Difficult PositionScanning the Patient Sitting Uprightsurement when the midsagittal view is unachiev-Measuring the NT requires a perfect midsagittalable in the standard supine maternal positionview of the cervical and thoracic portions of the(Figure 1). This is particularly helpful in obesefetus with visualization of the nasal tip as well aspatients because the scan window when thethe third and fourth ventricles of the fetal brain.patient is upright rises above the panniculus.The goal of the scan is to obtain this midsagittalview no matter what the fetal position. In cases inThe Simultaneous Transvaginal andwhich the fetal or uterine position precludes aTransabdominal Techniquemidsagittal view when the mother is in the stan-The second technique involves scanning bothdard supine position, sitting her up at 75° to 90°transvaginally and transabdominally simultane-results in a change in orientation of the uterus,ously. Although scanning transvaginally alonethus allowing the ultrasound beam to enter thewill sometimes result in a midsagittal view, oftenuterus from the fundus. The transducer is placedthe fetus has spun around, and the NT is still notjust under the umbilicus and angled caudad tomeasurable transvaginally. While scanning trans-image the fetus at 90° from the original positionabdominally, we use the endovaginal probe towhen the patient was supine. This change isstabilize the uterus or to push the uterus towardoften enough to obtain an adequate NT mea-the anterior abdominal wall (this works especial-Figure 1. A, Upright positioning of the patient and transducer when using the “sitting-up” technique. B, Fetus in the coronal plane,in an awkward position for the NT measurement when the patient is supine. C, Same fetus when the patient is sitting up and theultrasound beam enters the uterus from the fundus. Note that the fetus is now seen in the midsagittal plane. D, Fetus in the mid-sagittal position showing the position for the NT measurement and caliper placement.ABCD1262J Ultrasound Med 2010; 29:1261–1264298jum_online.qxp:Layout 1 7/20/10 10:35 AM Page 1263Bromley et ally well if the uterus is retroverted). Depending onmidsagittal view of the fetal head and neck is notthe fetal movement and position, the sonologistalways obtainable with the patient in the stan-or sonographer can toggle back and forthdard supine position. Additionally, a recentlybetween the transabdominal and endovaginalemptied bladder may contribute to a less thanimages, displaying views that are oriented atoptimal fetal position. We have found that whenright angles to each other. Using a simultaneousstandard techniques of turning the patient fromtransabdominal and endovaginal approach, aside to side fail, placing the patient in a sittingmidsagittal orientation of the fetus should beposition will provide a new view into the uterus,achievable in most cases (Figure 2).at 90° from the initial attempt. If this maneuverdoes not suffice, the sonographer can then try theConclusionstransvaginal approach. If the appropriate fetalThe success of fetal sonographic NT measure-image is still not obtained, the patient should bement depends on our ability to view the fetusrescanned transabdominally while the vaginalfrom multiple directions because the perfectprobe is still in place and can be used to manipu-Figure 2. A, Positioning of the patient and transducer for the simultaneous transvaginal and transabdominal technique. Note thatby angling the vaginal probe down, the uterus can be pushed up toward the abdominal probe. B, Transabdominal image of a first-trimester fetus referred for NT measurement. Note that the fetus is very deep within the maternal pelvis because of a high maternalbody mass index. C, Transvaginal imaging of the fetus provides a much clearer view. However, the fetus is not in a midsagittal view;therefore, the NT cannot be measured. D, Transabdominal scan of the same fetus where the vaginal probe is in situ and is being usedto push the entire uterus closer to the abdominal wall, thus resulting in a much clearer image. Note that the NT is easily seen andmeasured, and the nasal bone is also identified.ABCDJ Ultrasound Med 2010; 29:1261–12641263298jum_online.qxp:Layout 1 7/20/10 10:35 AM Page 1264Nuchal Translucency Measurement on the Fetus in a Difficult Positionlate the orientation of the uterus. We use theseimaging techniques in fetuses where the standardtransabdominal approach is unsuccessful inobtaining a perfect midsagittal view. Previously,these patients would have required another eval-uation at a later time. Since introducing this scan-ning protocol into our practice, we have been ableto obtain an NT measurement successfully with-out a need for repeat scanning in the last severalhundred patients. This brief communication issimply meant to introduce these techniques tohelp the practitioner obtain an NT measurementwhen the fetus is in a difficult position. We did notaddress how often these techniques were requiredto obtain an NT measurement. A prospectivestudy is needed to determine the frequency withwhich each of these techniques is used in a largeclinical practice.References 1.ACOG Committee on Practice Bulletins. ACOG PracticeBulletin No. 77: screening for fetal chromosomal abnor-malities. Obstet Gynecol 2007; 109:217–227.2.Wax JR, Pinette MG, Cartin A, Blackstone J. The value ofrepeated evaluation after initial failed nuchal translucencymeasurement. J Ultrasound Med 2007; 26:825–828.3.Thornburg M, Mulconry M, Post A, Carpenter A, Grace D,Pressman EK. Fetal nuchal translucency thickness evalua-tion in the overweight and obese gravida. UltrasoundObstet Gynecol 2009; 33:665–669. 1264J Ultrasound Med 2010; 29:1261–1264