Monday, 24 March 2014

When do you actually need PGS/CCS test?

It is important for every patient to know that female uterus has natural selection process that prevents implantation of abnormal embryos and majority of chromosomally abnormal embryos have reduced survival period and are rejected in early stages of development. However, in older women the eggs are often chromosomally abnormal - and the percentage of eggs with a chromosomal abnormality increases with increasing female age. 

The idea of testing the chromosomes before transfer is to implant effective embryos with normal chromosomes and reject the abnormal ones. Women with failed IVF cycles are susceptible to understand the need of these tests. The unilateral thinking that the test would ascertain their chances of conceiving would further expose such patients to trauma.

There are certain facts that patients need to know before undergoing the tests. The obsolete FISH method, which was limited to the testing of only 10 or 12 out of 23 chromosomes, provided the room for PGS/CCS (Comprehensive Chromosomal Screening) to enter the technology-era. Without much paddle, these methods embraced with much acceptance without drilling into the risks surrounding the method. To diminish the risks of IVF failure, CCS was used to avoid a failed transfer, miscarriage or a pregnancy complicated by an abnormal fetus such as Down’s syndrome.

In simple definition, Preimplantation Genetic Screening (PGS) is the process of ensuring the right number of chromosomes and check structural abnormalities in the chromosomes by screening the embryos. The process is also called aneuploidy screening.

PGS is thought to increase success rates for IVF in women over 35, as well as those who have suffered repeated IVF  or recurrent miscarriage. Comprehensive Chromosomal Screening (CCS) is a term used to refer to a type of PGS/aneuploidy screening. The method allows for the evaluation of all 23 pairs of human chromosomes on a single cell.

With CCS, there are five to 10 cells retrieved from a Day 5 or 6 embryos (blastocyst). The embryo has to be frozen while waiting for the result, and then in a separate cycle, the normal embryo is thawed and transferred. Biopsying a Day 5 embryo increases the accuracy of this testing and minimizes the potential damage that a biopsy can cause on an embryo because it has several hundred cells by then.

Patients are uncertain whether tests of early embryos before transfer will increase the chance of a successful pregnancy. But, the chromosomal screening of the embryos prior to choosing the best ones might damage the embryos from the biopsy procedure, which increases risk of failure.

While these tests can help reduce risk for birth defects and miscarriage, certain lesser known risks surrounding the latest embryo testing methods should also be considered. The major concerns involve, the embryos could be traumatized by the biopsy procedure. So it is suggested for patients wedged in situations like, females above 38 years old, with repeated IVF failure (more than three attempts), screened with inherited genetic diseases, carriers of chromosomal translocations or have had recurrent miscarriages.

Dr Neeraj Pahlajani 

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