Q: When PGD is performed to determine any chromosome issues, can it be done on frozen blastocysts before transfer?
A: PGD (preimplantation genetic diagnosis) is best done on cleavage stage embryos (day three, when they are at the six-to-eight cell stage). PGD requires embryo biopsy, which involves the removal of one of the cells of the embryo. This cell is then tested. Usually the testing is done by FISH (fluorescent in situ hybridization) to look for aneuploidy or by PCR (polymerase chain reaction technology) to look for single gene defects.
Microarray technology may be practical at the single cell level soon, but it is not widely available at present. It takes time to do the testing (one to two days actually). That means if embryos are tested on day three, the results are available by day five, so a blastocyst (day five) transfer is done. Embryos need to be transferred by day five in order to get a good outcome in terms of pregnancy rates—if you biopsy a frozen thawed blastocyst that is a day five or day six embryo. If it takes one to two days to get the result of the test, it is then too late to transfer the embryo and expect a pregnancy to result. Embryos do not develop as well in culture for long periods as they do in a woman’s body. As a result, after this long in culture, they are out of synchrony with the endometrium and poorer in quality if they survive at all for that long. Most embryos will actually arrest in their development by then. I hope this helps.
Fertile Thoughts is published monthly. Each column features a real question from a reader, and we invite other readers to respond with their thoughts and insights by posting comments. If you have a question for Dr. Carlene Elsner, please send it to her care of the editor at laura@realgirlsmedia.com. Your question will be kept in the strictest of confidence.
Never miss a Fertile Thoughts column again. Just click on the author’s name at the top of the story, then select “Be notified when writer publishes” at the top of the page. We’ll send you an email as soon as a new column is published.
PREVIOUS PAGE
