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Re: risk recalculationFrom: David Nyberg (nyberg@u.washington.edu)Wed Jan 14 08:56:07 2004
There is good evidence that biochemical markers and ultrasound markers are independent. Also, most ultrasound markers are indpendent of one another. We have previously reported likelihood ratios for ultrasound markers as isolated findings, assuming that you also perform a systematic "genetic sonogram" in the same or similar manner, and the finding really is isolated (ie don't forget humerus length shortening). We showed that isolated EIF carries a Likelihood ratio of 1.8, or estimate as 2. This does not apply to asian populations however, because of the high prevalence of EIF among asian. Although a right sided EIF is considerably more unusual than a left sided one- and I'd be sure you are not identifying the moderator band rather than an EIF- I would not change the likelihood ratio based on this alone. On the other hand, bilateral EIFs definitely seem to carry a higher risk- we just don't know how to quantify that risk yet. So in this case, with the caveats mentioned, the risk should be no more than about 1:300 (606/2) and in fact a little lower than that if you use a LR of 1.8. In other words, the patient remains in the "low risk" category despite the finding based on the normal first trimester screen. You can still download or see an excel file that quantifies this at an educational website, http://www.fetalcenter. org hope this helps David On Wed, 14 Jan 2004, Patrizia wrote:
> dear colleagues
-- David Nyberg, MD 10401 E McDowell Mtn Ranch Rd #2-372 Scottsdale, AZ 85255 ph cell 480-797-0993 fax 480-512-8737 work 480-512-3850
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