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Re: OB: AFP/multiple marker datingFrom: viv souter (vsouter@yahoo.com)Wed May 5 11:10:24 2004
Hi Garry My experience is that when you use ultrasound dates for calculating 2nd trimester biochem risks, the labs use a different algorithm and computer program from that which they use if the dating is based on LMP; it is not just a function of three days difference in gestational age. I have reviewed lots of similar results as part of a research study and the LMP risks are quite substantially different from the ultrasound based results. If I were you I would contact your lab and check out what they do; most labs use LMP based risk calculation if the ultrasound gestational age is within 10 days or a week of the LMP dates. In my xperience therefore the initial risk would be the most commonly one to be used. Of interest I believe that in the FASTER study they based all the risk calculations on the first trimester CRL. Hope that helps Vivienne Souter OK, a quick curbside until I can research further. The patient is a CNM one, so this kind of fell into my lap late today. 20 YO P0 has an AFP triscreen done LMP makes her EDC 10/7/04 7 week scan makes her EDC 10/10/04 To me, that is excellent correlation, and the EDC we tell the patient is 10/7/04. 10/7/04 is the EDC used for the AFP. The report comes back--increased Down risk, 1/230 or whatever. The CNM has the lab plug in 10/10 for the EDC, and the recalucation is "normal risk" of 1/350. So. . . Which EDC should have been used initially? If it is the period EDC, what do the results mean? What's a mother to do??? Garry
-- Garry E. Siegel, M.D. Private Practice Roswell, GA
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