back to the list

Preimplantation Genetic Testing (PGD)

PGD testing

Clinical Features

The desire to have a child of one's own is not always as easy to fulfil as a couple might hope. Whether a pregnancy comes about naturally or if artificial means are needed depends upon many factors, for example, genetic predisposition or a couple's age. As conception becomes increasingly difficult, a number of medical advances have been made in recent years to help couples with fertility problems fulfil their desire to have children of their own.

It is estimated that about every second fertilised ovum contains aneuploidies (a failed distribution of individual chromosomes which are then either too many or too few in number). Many of these embryos abort prior to implantation; only a few survive long enough to be born. As a woman ages, egg cell maturation becomes increasingly imprecise.

Every normal cell in the body contains all 46 chromosomes in pairs, each pair consisting of one paternal and one maternal chromosome; ovum and spermatozoon each carry only one of these chromosomes. During maturation, surplus information is discharged from the ovum into so-called polar bodies. Polar bodies can be removed without damaging the egg cell. The most common method of analysing polar bodies has been Florescence-in-situ-Hybridisation (FISH), whereby individual chromosomes are detected under the microscope through a process of florescent dyeing. Due to its technical limitations, this method can only analyse failed distribution in a portion (5-10) of the entire 23 chromosomes. However, since aneuploidy can occur throughout all 23 chromosomes, thus frustrating or preventing nidation or a successful pregnancy, an analysis of all 23 chromosomes makes more sense, especially in cases where older patients have already undergone unsuccessful artificial fertilisation or have suffered repeated miscarriages.

Our lab performs polar body analysis (PKD) or trophoektoderm analysis (PID) based on Array-CGH (24sure, BlueGnome). With this system, the presence or absence of all 22 autosomes and gonosomes can be detected, thus making it possible to transfer to the uterus only those fertilised egg cells found to be without aneuploidy. Admittedly, it has not yet been possible to detect all failed distributions; however, the risk of implanting embryos with aneuploidy is greatly reduced. It is therefore assumed that this method of polar body analysis reduces rates of miscarriage; the cryopreservation of embryos with aneuploidy can also be avoided.

Diagnostic