Update on PGD/PGS
We know that the process of IVF is inefficient since the number of babies born per embryo transferred is relatively low, especially with increasing age. It is commonly believed that this is due to the large number of genetically abnormal eggs that we retrieve during an IVF cycle. Until recently, our desire to distinguish a genetically normal embryo from an abnormal one has not been matched by our ability to do so accurately. PGD/PGS has now been around for 20 years. During most of that time, a technology called FISH (Fluorescent In Situ Hybridization) was used. Due to the technical limitations of this procedure, we were only able to test half (12) of the chromosomes at best. Because of this, the accumulated data showed that we really weren’t able to improve the efficiency of IVF from this procedure. That of course makes sense since any one of the other 12 chromosomes could be abnormal and we wouldn’t know it. We probably transferred a lot of abnormal embryos thinking that they were normal when FISH was used. For that reason, I was never very enthusiastic about using FISH except in a few select situations.
Recently a new procedure called CGH (Comparative Genomic Hybridization) has become available which allows us to obtain information about all 24 chromosomes. We have been using CGH since late 2009 with much more success than when we were using FISH. This procedure gives us complete genetic information from a single cell obtained from the embryo in question. The results are available within 48 hours so that the normal embryos can be transferred without having to freeze them. We are finding a high rate of genetic abnormality in the embryos that are tested. For example, for women under 35 years of age, only 40% of the embryos biopsied were normal. For the 35-40 year olds, 18% were normal and over 40 years less than 1/10 are normal. I am very excited about using CGH because it appears from the results so far, that in time the data will probably show that PGS does improve the efficiency of IVF for certain groups of patients, especially those who are over 35 years old. We have had a few couples who have requested PGS in their first IVF cycle even though they were less than 35 years old, just to avoid having to do repeated cycles. Time will tell if this approach makes sense but so far, all of those couples have been successful.
PGD, the testing of an embryo for the presence of an abnormal gene causing a specific disease, is now applicable to over 1000 different disorders. Probably the most common disorders are Cystic Fibrosis, Hemophilia, Sickle Cell disease and Tay-Sachs but there are many more lesser known ones that we can test for as well. PGD can be performed along with PGS for chromosome screening on the same single cell.
If you would like to know more, check out out website. I have recently updated the section about PGD/PGS to include a detailed explanation of how CGH works.
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Reply #5159 on : Sun February 05, 2012, 00:57:56
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Reply #5158 on : Sun February 05, 2012, 00:01:36
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Reply #5157 on : Sat February 04, 2012, 22:43:55
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Reply #5156 on : Sat February 04, 2012, 22:21:02