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Fw: Nuchal TranslucencyFrom: Allen Worrall (jworrall@acsalaska.net)Sun Aug 18 23:04:36 2002
>----- Original Message ----- On Sun, 18 Aug 2002 10:29:08 -0800 "Allen Worrall" <jworrall@acsalaska.net> writes: Dear Dr. Ewida - Nuchal translucency must be done when the fetal crown rump length (CRL) is between 45 mm and 85 mm. This is ~11 weeks 0 days to 13 weeks 6 days. A proper nuchal translucency can be obtained by both transvaginal and transabdominal scanning. Most experience sonographers have more success transabdominally because one has more room to maneuver the transducer on the abdomen than in the vagina. However, the imaging is generally more clear transvaginally. A valid nuchal translucency should be obtained on a midsagittal view of the fetus. It does not matter if the back of the fetal neck is toward the transducer or away from the transducer, but the sound beam must "slice" the fetus down the middle. Also the back of the neck must be or should be orthogonal to the sound beam, so that a good specular reflection is obtained of the fetal skin and underlying tissues. One of the pitfalls for the inexperienced is to measure the distance from the amnion to the skin and think they are measuring nuchal translucency. If the back of the fetal neck is lying on the amnion, we will wait for the fetus to jump up, and freeze the frame so that we are sure we are not measuring amnion. We know we have a good midsagittal view if we can see a very nice facial profile, and the spine is either straight up or straight down. The measurement cursors must be placed very carefully and the image depth must be reduced, and the image enlarged, so that the fetus is occupying most of the available screen "real estate". These are all factors that one learns when one attends the one day course in the 11-14 week scan given by The Fetal Medicine Foundation of London, Professor Kypros Nicholaides. I have some words about nuchal translucency on my web site http://www.obgynsono.com If your wife's scans were done at the ob or radiology departments at Hahnamann, it is very likely that the persons doing the scans were familiar, trained, and experienced in nuchal translucency measurements. If the second measurement were done by an emergency medicine specialist in the ER, perhaps that is the measurement that might be wrong. A nuchal translucency of 4 mm is pretty obvious on the scan in most cases; even if one were unable to obtain the optimal view, one would be able to see that there was edema at the back of the neck, even on an axial view of the neck. You probably need to talk to the doctors involved with your wife's care to determine which of those two nuchal translucency measurements is the most valid, and should be used to calculate risk of Down. The process of calculation: refer to a table of expected values for CRL; divide the found NT by the expected NT to obtain a Multiple Of the Median. Refer to a table to convert the MOM to a likelihood ratio. This LR can be used to modify your wife's age-related risk of Down. Increased nuchal translucency can be related to cardiac problems and other things, but the risk calculations apply only to the risk of Down, as far as I know. I have seen measurements that have changed quite a bit in a matter of a week or two. I do not know if a change of 1.5 mm in four days is unusual. I have a very low volume of prenatal scans compared to many of the large centers. In the past few years that I have been doing nuchal translucency I have seen 4 cases of increased nuchal translucency, and not one of those babies had anything wrong. I do not say that to imply that nuchal translucency is not worthwhile. I say it to give you some hope that things might be OK despite the increased nuchal translucency. The false positive result is one of the prices we pay for the advantages of prenatal sonography. Terry DuBose has given you good information and good references. If I can be of any more help, please do not hesitate to contact me. The best of luck.
-- Allen Worrall
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