At Thames Valley Fertility we offer genetic testing through our collaboration with Reprogenetics UK. There are two types of genetic testing; PGS (screening) is used to screen the embryos for any random imbalances in chromosome numbers, and PGD (diagnosis) is used to detect specific genetic disorders/diseases that the family are at risk of.
If you’d like to discuss the genetic diagnosis options available to you for your IVF cycle, please contact us.
Chromosomal abnormality is one of the most common causes of unsuccessful pregnancy. If an embryo has too many or too few chromosomes (a condition called aneuploidy) this can have a serious effect on its chances of developing normally into a fetus and then a baby. In many cases, embryos with the wrong number of chromosomes stop growing by themselves, and this unfortunately often results in miscarriage.
This is no less common with IVF treatment. However, the IVF process enables us to monitor the development of multiple embryos at the same time. We can provide various levels of genetic screening during treatment, to help us select embryos with normal chromosomes, which have the best chance of developing into a healthy pregnancy.
Genetic mutations, sometimes passed down from parents, are another cause of unsuccessful pregnancy. Pre-implantation genetic diagnosis is used when a serious genetic disease could be passed from parent to child. There are two techniques: karyotyping, and conventional pre-implantation genetic diagnosis. We are particularly pleased to be able to offer karyomapping as, unlike with conventional PGD, embryos can be screened for chromosomal abnormalities as well as a certain genetic mutation, thus increasing the likelihood of a healthy on-going pregnancy. Conventional PGD is used where the mutation is new and not present in either of the parents, or where we are unable to obtain DNA from other family members who have the same genetic mutation.
Pre-implantation genetic diagnosis can also help couples who have discovered that they have a balanced translocation or inversion. A special high-resolution array Comparative Genomic Hybridisation test can be used to select normal embryos.
Key features of the single-gene PGD service
*Disorders must be licensed for testing by the HFEA.
A full list of approved disorders is available at: http://www.hfea.gov.uk/cps/hfea/gen/pgd-screening.htm or contact us for advice.
The first few stages of an IVF cycle that involves PGS or PGD are no different from any other. The only difference is that for PGD cycles the eggs are always fertilised using intracytoplasmic sperm injection (ICSI), regardless of how good the sperm sample may be. The use of ICSI reduces the risk of DNA contamination derived from sperm when testing for specific genetic disorders with PGD.
The embryos that develop will be cultured and examined and you will be advised if they are suitable for biopsy which will take place on day 5 or day 6. Only embryos at the Blastocyst stage (Day 5 or 6) can be tested by taking a small sample of cells (called a biopsy) using a needle. The area of cells biopsied is purposefully taken from the cell population which will go onto make the placenta so that we do not damage the cells that will make the baby. The biopsy samples are placed in tubes and sent to the genetics laboratory. The genetic test takes 4 weeks to process and so your embryos are frozen until we have the result.
Scientists working in the laboratory carry out the genetic test on all of the samples received.
For PGS testing the results indicate how many copies there are of each chromosome, revealing any abnormal embryos. PGS does not require additional blood tests prior to the IVF cycle.
For PGD testing the results indicate if the embryos carries any copies of the affected gene associated with the genetic disorder being tested for.
Once the genetic results are known an embryologist will call you to discuss these with you and plan your next appointment for you accordingly. Any suitable embryos can then be replaced in a frozen embryo replacement cycle.