Genetic diagnosis (PGD)

Around 50-60% of one-off miscarriages are caused by chromosome abnormalities. If testing reveals that a genetic abnormality may be responsible for recurrent miscarriage, one option for future pregnancies is pre-implantation genetic diagnosis, or PGD.

What is PGD?

PGD involves having a cycle of IVF, then testing the embryos for the genetic disorder. Only embryos revealed to be free of the disorder are then considered for transfer to the uterus.

In many cases, this is considered preferable to continued attempts at natural pregnancy followed by miscarriage.

More about IVF and PGD can be found on the Sydney IVF web site.

Types of genetic disorders

There are several types of genetic disorder that may be responsible for recurrent pregnancy loss. More about these can be found on the Sydney Genetics web site.

Analysis

Sydney IVF scientists can use a number of different methods to analyse the biopsied cells.

For chromosome analysis, Sydney IVF uses a technique called comparative genome hybridisation or CGH to analyse biopsied cells.

CGH has many advantages over the outdated FISH technique - the main one being that it can accurately visualise ALL of an embryo's chromosomes, rather than 9 that FISH allowed.

To begin, the biopsied cells are subjected to whole genome amplification (WGA), a process that results in the production of multiple copies of the DNA being investigated.

The CGH techniques then requires 72 – 120 hours of laboratory time to reveal the chromosome status of the embryo and it is therefore a requirement that all embryos undergoing CGH analysis be vitrified (stored in liquid nitrogen) whilst the analysis is conducted.  Sydney IVF have been vitrifying day 5 blastocysts clinically since January 2006.

Embryos found to have a normal chromosome complement can then be transferred in subsequent frozen embryo cycles. 

If the problem is at a gene level rather than chromosome it is more common to use PCR.

PCR makes millions of copies of a part of the DNA code, which allows us to see whether this part of the DNA in the sample is normal or mutant.

Images:

Top: Fluorescently labelled DNA from the cells biopsied from a human embryo.  Our cytogeneticists capture 3 fluorescent images and overlay them to produce the result.

Right: The analysis data generated by our cytogeneticists and computer system shows us all the embryo’s chromosomes. The close up shows a trisomy of chromosome 18.