Preimplantation Genetic Diagnosis (PGD)

Preimplantation genetic diagnosis (PGD) is testing of embryos for a genetic condition, usually to exclude embryos that, if they implant, would result in a baby affected by the genetic condition.

Patients come to consider PGD for a variety of reasons. Their paths in coming to the option of PGD to reduce risk in future child(ren) are sometimes simple but are very often complex and difficult.

Which Patients use PGD?

I have treated patients who themselves have a genetic condition and wish to (virtually) eliminate the risk that their child(ren) will inherit the same condition as well as patients who have had a child diagnosed with a genetic condition and have subsequently discovered they are both ‘silent carriers’ (autosomal recessive) and choose to then use PGD to (virtually) eliminate risk in subsequent child(ren). Increasingly I am seeing patients who through genetic screening have been informed that their particular combination of genetics puts their future child(ren) at a high risk of being affected by a genetic condition.

Regardless of how complex, simple, devastating or serendipitous the ‘back story’ that leads patient patients to PGD, the process of PGD is fairly straightforward as long as we know the gene(s) we are looking for.

Tailoring PGD to your needs

Before commencing PGD I will link you in with a Clinical Geneticist (Specialist Genetics Doctor) and the Monash IVF PGD science team to ensure we have or can ‘build’ a test to suit your particular genetic needs. Once the validity of an existing test has been established, or a new test ‘built’ IVF proceeds in a fairly standard way (although there are some cycle modifications that I usually make to reduce side effects compared with a standard IVF cycle).

Growing Embryos using IVF

Women take medications to ‘grow’ a batch of ooctyes (eggs), they are collected, fertilised and then the embryos are grown in culture. The shells of the embryos are weakened by a precise laser to speed up hatching. Embryos are regularly assessed (via images taken by the incubator, the embryos are not disturbed). Embryos that are hatching from their shell (a normal process) and are suitable to biopsy have a few cells taken from their outer layer (the trophectoderm, future placenta). Those cells are taken for analysis. The embryo naturally ‘seals’ the gap from the removed cells and the embryo is cryostored (frozen).

Analysing the Embryos

The embryo biopsies are analysed for the genetic condition, usually to a 99% degree of accuracy. In addition to the genetic condition in question many patients also elect for the chromosomes of embryos to be screened for additional conditions. This is done to minimise the use of embryos that do not have potential to result in an ongoing pregnancy and to reduce the risk of Trisomy 21 (Down Syndrome) and other non-lethal chromosome differences. This can be done at the same time without requiring further biopsies.

What happens next?

Once the biopsy result is known and there is an embryo to transfer the process is relatively simple. A woman’s menstrual cycle is tracked to determine day of ovulation and an embryo is transferred, synchronising timing to her natural cycle. In women who do not ovulate regularly ovulation is either induced with medication or hormones are given to mimic the natural cycle and prepare the uterus for embryo transfer.