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Re: Seeking for further studiesFrom: Allen Worrall (jworrall@alaska.net)Sun Aug 14 20:00:04 2005
Thanks Terry. I can see that I am going to have to look into this, both for the ultrasound machine I am using, and the reporting software. Allen
> ----- Original Message ----- "Correct me if I am wrong, but I believe the Hadlock and Shepard fetal weight tables do NOT use HC, at least the tables that I use. " Well, I would not say you are wrong, depending upon which Hadlock formula used. Shepard's variation on the Warsof fetal weight estimation does not use the HC, only the BPD and AC are used in the Warsolf and Shepard formulas. However, Hadlock published several formulas including one that used the transverse Head Circumference, Abdominal Circumference and the femur length (Hadlock FP, Harrist RB, Carpenter RJ, et al: Sonographic Estimation of Fetal Weight. Radiology 1984; 150:535-540.) This research compared seven different formulas, but the three parameter model was just as good as the four parameter model that also included the BPD. In 1995, I looked closely at this issue and the following quote is from FETAL SONOGRAPHY, W.B. Saudners 1996, p. 127. "There have been many studies of the sonographic estimation of weight. Several tables have been published. The Kurtz and Goldberg reference manual of 1988 for sonographic obstetrical measurements listed 95 references on fetal weight alone, and more have been published since then. One of the best known is the Shepard, et al variation of the Warsof Table, see Table 7-10.94, 95 It should be noted here that the regression formula published in association with the table in the original Shepard article has two different typographical errors which produce inaccurate results., Unfortunately, these typographical errors have been perpetuated by almost every reference to that article since its publication. One letter to the journal pointing out one of the typos left in the second error.101 The formula is printed correctly at the top of Table II of the article, but incorrectly on the first page and in the more obvious location at the top of the table used for weight estimates. This commonly used table estimates weight based upon the BPD and AC measurements. " So you can see that it really can make a difference in what formula/table is included in the machine you are using. If you do not know which formula is used, and just as important, you must know how the researcher measured the parameters, especially the head. At this date there are fetal head measurements that are leading-edge to leading-edge, mid-edge to mid-edge, and inter-skull measurements. This becomes very important in a large institution that may have numerous different machines that may use different parameters for estimating size/age/weight. You must know how this research was done for EVERY MACHINE, or you will get systematic errors on different machines. I am quite sure that this one fact alone is the reason that sonography has such a poor public image for accuracy. I think sonography is much more accurate than it is given credit for being, but there are so many different ways of doing things, it is very difficult to be consistent from machine to machine... even when the sonographer believes they know what they are doing. We need to have some study and standards of this issue. Terry
-- Allen Worrall <jworrall@alaska.net> wrote: I agree. In fact, even when an ultrasound machine and a reporting software say they are using the same table, I think there may be differences in interpolation when a measurement falls between one of the points listed in the table. Or perhaps it is the way the values are entered in the table.
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