Why is PGS not suitable for everyone with recurrent pregnancy loss? Part I

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The heartache of a miscarriage or recurrent pregnancy loss (RPL) can be almost debilitating for a lot of couples trying to start a family. Many times they look to assisted reproductive techniques such as in vitro fertilization (IVF) for assistance after two or more pregnancy losses. And while the odds of a successful live birth may somewhat rise with IVF attempts, there is much discussion underway regarding whether or not to commence pre-implantation screenings (PGS), a procedure that determines and evaluates chromosomal abnormalities in embryos before transfer, thus offering couples the chance to use only viable embryos during transfer to better their chances of conception and, ultimately, a healthy baby.

When discussing PGS, it is important to have in mind that couples longing for a family and already having experienced RPL should not perceive PGS as an universal solution to their problem. In fact, PGS is relevant for less than 50 % of RPL cases. Pregnancy loss is often not related to the embryo at all, but rather to issues in the uterus. Hence it is very important to clarify the root causes of RPL with your doctor before committing to such procedure.

What’s involved in a PGS and PGD procedure?

During a PGS, an embryo biopsy is performed on either day 3 (cleavage stage) or day 5 (blastocyst stage) of the growth cycle or embryo development. During the biopsy, an embryologist carefully removes one or two of the cells from the embryo.

All twenty-four chromosomes are examined, including the twenty-two non-sex chromosomes and the two sex chromosomes (X and Y) before an embryo transfer to the uterus commences. PGS screens and diagnoses extra chromosomes as well as missing chromosomes.

And then there is PGD – Pre-implantation Genetic Diagnosis that screens for a single-gene defect that could possibly lead to genetic disorders like cystic fibrosis. Even a couple who carry Tay-Sachs disease, (a rare inherited disorder that will progressively destroy nerve cells in the brain and spinal cord) could be more selective in embryo transfer and avoid using any embryos with the disease present in those cells. This comprehensive evaluation of embryos can be obtained prior to fertilization.

Another aspect of the test can provide information on gender, but most of the time this is not of importance to couples with recurrent pregnancy loss. Their primary concern is  to conceive and have a healthy baby.

Chromosomal abnormalities and why are they important

In humans, every cell usually has 23 pairs of chromosomes within it, for a total of 46. The 23rd set known as the sex chromosomes is the only differentiator and determine the sex. The first 22 pairs are called autosomes and are the same within men and women.

But when chromosomes don’t match up correctly, they are considered abnormal.

So, what is a chromosomal abnormality? There is a number of answers to this question. To start, embryos that have an abnormal number of chromosomes in a cell are known as aneuploid. An extra copy of chromosome number twenty-one would result in a child with Down’s syndrome. Chromosomes that are arranged incorrectly are known as translocations – most balanced translocation carriers are healthy and are not symptomatic, however, an estimated 6 % may pass on congenital irregularities, intellectual disabilities or even autism.

There’s a few more important things you should know about PGS and its attributes. We’ll talk about them in the two following articles, which focus on who is PGS suitable for, the latest findings as well as some practical information about actual undergoing the procedure.

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