Preimplantation Genetic Screening - Like all things, there are Pros & Cons

There are a number of factors which prevent women conceiving when they want to.  In a perfect world, across all ages, the natural conception rate is about 20-25% per month.

A major reason for this relatively low back ground rate of conception is that, depending on a woman’s age, between 35% and 60% of embryos which form, either naturally, or with IVF, are abnormal.

At around 35 years of age, 50% of embryos have an abnormal chromosome make-up.
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When a woman has IVF, it is now possible to test embryos’ chromosomal make up to assess the likelihood of them being normal.  This process is called Preimplantation Genetic Screening, or PGS.

In the United States, 70% of IVF cycles involve PGS.  In Australia, the rate is 15%, and climbing.  Whilst this may seem like a basic and logical step to increase the likelihood of having a baby, there are a number of important matters to consider before deciding to use PGS in your IVF cycle.

The first point to consider is that the process of testing embryos can’t make them normal.  When a group of embryos are formed from a fresh IVF cycle, they have a predetermined outcome, and PGS can’t change this.

Next, the PGS testing process does not always generate a useful answer regarding whether the embryo is normal.  This is due to the testing process sometimes failing, and the occurrence of “mosaicism” in an embryo.  This means that an embryo can have two, and sometimes three “cell lines” which may have different chromosomal make up.  In this situation, depending on cells analyzed, a predominantly normal embryo may be called abnormal, wasting the embryo.

Additionally, the process of performing embryo biopsy has the potential to damage and stress an embryo, reducing the likelihood that a normal embryo will implant and grow.  

Finally, whilst it is generally true that chromosomally normal embryos “look” the best under the microscope, this is not always the case.  Hence, when an embryologist selects an embryo, or number of embryos for PGS on the basis of their appearance, and score, there may be some embryos, which don’t score as well, which may have a normal chromosomal make up, and potential to generate a pregnancy.  Because PGS is expensive, scientists try to be “selective” when choosing embryos to test.  In order to have PGS, a woman needs to have at least 3 high quality, day 5 embryos.

There is no doubt that there are a number of women and couples who will benefit from PGS for their embryos.  A typical example is a woman who develops a large number of normal looking, high scoring embryos, who doesn’t conceive after a number of embryo transfers.

After PGS, the pregnancy rates per embryo transferred increase significantly, because, theoretically all embryos transferred are normal.  However, the cumulative pregnancy rate, and live birth rate, PER Oocyte collection cycle, in fact, decreases.  This is because normal embryos may be lost, discarded, or damaged during the whole PGS process.

If you wish to discuss PGS further, consult your Ballarat IVF or South West Fertility IVF specialist to see if it will be of any benefit to you.

All the best
Russell

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