For over twenty years it has been possible to test embryos for chromosomal abnormalities during an IVF cycle to identify the embryos with the best chance of developing into healthy babies. This process is called Pre-implantation Genetic Screening (PGS). The technique used until recently for PGS is fluorescent-in-situ hybridisation (FISH). Unfortunately, with FISH it was possible to test only a fraction of the chromosomes (up to 10 out of the 23). It has also been shown to sometimes deliver inaccurate results. A new technology called Array CGH is now available to test all 23 chromosomes in a single cell or blastomere.
Up to 40-80% of human embryos may contain abnormal number of chromosomes (known as ‘aneuploidy’) depending on the woman’s age. Chromosomes are structures found in every cell of the body that carry the genes in the form of DNA. Normally humans have 46 chromosomes arranged in 23 pairs. The first 22pairs are the same for both males and females while the last pair, called the sex chromosomes is either XX in females and XY in males. Most chromosomally abnormal embryos will not implant and if they start to implant are most likely to miscarry. A major cause of failure of embryos to implant or miscarry is chromosomal abnormality in the embryos. Array CGH makes it possible to screen eggs or embryos to enable us to select only chromosomally normal embryos for transfer into the woman’s uterus, thereby improving the chances of successful implantation and reducing the risk of miscarriage leading to the birth of a healthy baby.
Assay CGH is performed on
a) Eggs: testing the chromosomes in the polar body of the egg
- testing chromosomes of a cell (blastomere) of a day 3 embryo
- testing the chromosomes of a blastocyst by removal of trophoblast cells
The circumstances of each couple are different and a clinical judgement will be needed, with discussions at your consultation, to assess which approach would be most appropriate .
The clinical benefits of PGS by array CGH remain an active area of research. Aneuploidy can occur in any embryo from a couple by chance although some couples are at a higher risk.
Array CGH may be particularly beneficial for the following groups:
1 Women over 35 years of age
2 Couples experiencing recurrent miscarriage
3 Couples experiencing recurrent IVF failure
4 Women who have had termination of one or more chromosomally abnormal pregnancies
If you fall into any of these categories and feel that Array CGH might be of benefit to you, then you can discuss it further with Mr Ndukwe or Dr Rojas at consultation.