Experts in Preimplantation Genetic Diagnosis

What you need to know before considering PGD for gender determination

PGD is a complex procedure:

Preimplantation Genetic Diagnosis (or PGD) requires expertise in genetics, clinical embryology, microsurgery to remove one or more cells from embryos (biopsy), and non-surgical transfer of embryos into the uterus. Needless to say, the laboratory where the chromosome analysis is done must be licensed and its staff must be highly qualified. Each laboratory must establish a technical “error rate” for the tests they perform. This refers to the frequency with which abnormal embryos are diagnosed as normal or normal embryos are diagnosed as abnormal as a result of technical errors. As a patient, you should get as much information as possible regarding the test error rate at the PGD laboratory to which the IVF center refers cases; this rate should be publicly available. Error rates above 5% are considered unacceptable.

Embryo biopsy may negatively impact pregnancy rates:

A recent study1 shows that the removal of two cells from an embryo on day 3 of development in culture results in lower chances of pregnancy than if one cell were to be removed. But not removing any cells from the embryo for any purpose is probably better than removing one cell! If you have decided to undergo PGD for gender selection after day-3 embryo biopsy, you are accepting a small decrease in your chances of conceiving.

Another option for obtaining genetic material from the embryo is through blastocyst (day-5) biopsy. At this stage the inner cell mass, which will give rise to the fetus, has differentiated from the trophectoderm, which will later on develop into the extraembryonic tissues. Biopsy at this stage involves the removal of a number of cells (3-10) from the trophectoderm. This type of biopsy is advantageous in that no cells are extracted from the inner cell mass and also, in contrast to day-3 biopsy strategy, this method obtains multiple cells for carrying out PGD, which theoretically leads to improved accuracy. Furthermore, blastocysts are more robust than earlier embryonic stages and tolerate biopsy exceptionally well

The ethics of gender selection:

Gender selection is considered by some to be unethical; it is unlawful in Europe. It is argued that selection can lead to gender discrimination/imbalances or selection inevitably leads to destruction of potentially normal embryos of the unwanted gender. Reprogenetics has studied the use of PGD for gender diagnosis2 and has reached the conclusion that at least in the US the first argument does not apply because the technique is overwhelmingly used for family balancing purposes. However, with respect to the second argument, Reprogenetics encourages couples seeking this procedure to freeze or donate the normal embryos of the unwanted gender provided that they have been screened comprehensively either for all chromosomes.

If you decide to use PGD for gender selection, the method of choice is one that allows screening for all chromosome abnormalities (aneuploidies) at the same time.

By analyzing all chromosomes with array CGH through comprehensive chromosome screening (CCS), you may increase the chance of conceiving and carrying the pregnancy to term than by analyzing only the sex chromosomes (chromosomes X and Y) and/or just a few chromosomes.  The risk of conceiving a child with Down syndrome and other genetic abnormalities will also be considerably reduced if not entirely avoided. A recent randomized pilot study using aCGH showed a considerably high clinical pregnancy rate (70.9%) which was found to be significantly higher than the clinical pregnancy rate calculated for patients whose embryos had not gone through CCS (45.8%).


For reference:

1 Goessdens et al., Human Reproduction, 2008

2 Colls et al, 2009, Reproductive Biomedicine Online