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Anomaly scan, Serum testing, Down Syndrome and LateralFrom: James Smeltzer (James.Smeltzer@wellstar.org)Thu Jul 10 04:42:51 2008
Hi! All the cells of the CNS are lining cells of the wall of the tube that started there, migrated out to their final position and did what they were supposed to do, based on where they came from and other factors.
>From a CNS perspective we are all totally tubular! It only stands to reason that the starting mass of cells outside the tube is small, and grows as more join them. This is the way of the tube. Allen, 10-15mm seems a bit generous for the LV tube diameter at the atrium at 13 weeks, since as the BPD is only 20mm and has to include one side of the skull and the entire brain, and the two LVs are at a slightly higher - and narrower - level of the brain (but still have SOME brain substance at 13 weeks. A nuchal translucency of 2.6mm at 13 weeks (~CRL 67) is sufficient to discuss/offer an amnio or CVS and fetal echo, or serum testing, tqargeted sonogram (our preferred route), as the odds ratio for Down Synd is about .75/.05. or about 15 fold the baseline age and other screening risk (Snijders & al, Lancet 1998; 351:343-6). Yagel & al Ult. (Obstet. Gynecol 11:262, 1998) come up with more conservative numbers, and if your normal data fit their curve, you are right not to routinely offer an amnio to a womal under 31, as their predicted nuchal lucency is 2.6 mm. (Odds ratio of ~2 - not sure of their Down results). I am not recommending everyone rely as heavily on dysmorphology as we do, as there is a learning curve, amnio is 100% (99.4%) reliable and we do a ridiculously low number of amnios - with a ridiculously high positive rate. But looking never killed a baby. I would definitely look for tricuspid regurgitation, brachycephaly - which can be seen early - short femur, and humerus, and an absent nose bone, at least. Of course an AV septal defect alone would be sufficient to warrant an amniocentesis. Personally, in our hands, serum markers have helped to identify Down syndrome only once in the absence of a suggestive sonogram, but have - with quad screen - gotten to an acceptably low false positive rate, low enough to raise the odds, and significantly increase the detection of Down syndrome in the absence of early careful sonography. Know your results and your normal curve for NL as these are essential for interpretation of results. (I still do not understand how we get such different normals. Maybe we should all take the same course;^) Hope this helps! Jim Smeltzer
-- James S. Smeltzer, MD, FACOG, SMFM Consultant, Maternal Fetal Medicine Wellstar Physicians' Group Northwest Women's Care 787 Campbell Hill St Marietta GA 30060 James.Smeltzer@wellstar.org VM 678-290-3035 Off 770-528-0260 Page 404-318-3451
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