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Pre-Implantation Genetic Diagnosis

Tests such as amniocentesis can be done during early pregnancy to try to detect genetic disorders in the foetus. A positive finding from the amniocentesis means the couple are then faced with the difficult decision of whether to continue or terminate the pregnancy. The development of Preimplantation Genetic Diagnosis (PGD) and embryo biopsy means there is now an alternative to amniocentesis.
PGD treatment involves the female partner undergoing a stimulated IVF cycle in order to obtain a number of eggs (oocytes). The oocytes are then inseminated using a sperm sample collected from the male partner. The fertilised eggs, now called the embryos, are allowed to develop in culture until they reach 8-10 cell stage. This will usually take 3 days after the removal of the oocytes from the ovary. Using micro-manipulation techniques, one or two cells are removed from each embryo for genetic testing. This procedure is called embryo biopsy.

The removal from the embryo of one or two cells called blastomeres has been shown to have little adverse effect on the potential of the embryo to create a normal pregnancy, as each cell in the early embryo has the potential to be a total human being.
The detection of any abnormality at the gene level requires the latest molecular techniques such as polymerase chain reaction (PCR) and fluorescence in situ hybridisation (FISH). Only embryos, which the above tests have shown to contain normal chromosomes, are transferred back into the women's uterus.

PGD can be successfully performed for detecting chromosomal disorders, such as Down's Syndrome or Turner's Syndrome which are more commonly found in foetuses of mothers of advanced age. The technique which is most commonly used for this purpose is the FISH technique involving specific probes for chromosomes X, Y, 13, 18 and 21. For example, the Down's Syndrome foetus has three chromosomes 21 rather than two. Determination of the sex of an embryo is attempted for selection of female embryos for transfer in X-linked disorders such as the Haemophilias and Duchenne Muscular Dystrophy. In these conditions, the female carries the gene but only the male is affected by the disorder. Consequently only the female embryo is transferred into the uterus.
Using single-cell PCR (which is a molecular technique allowing the amplification of a gene of interest from one copy to millions of copies) it is possible to detect single-gene disorders such as cystic fibrosis, alpha 1 antitrypsin deficiency, retinitis pigmentosa, haemophilias A & B, thalassemia, Gancher's, Tay Sach's and sickle cell disease.

The PGD services at The Wesley IVF Service are offered to the following patients:-
1.Patients with a family history of genetic illness.
2. Patients who have had repeated miscarriages or multiple IVF failures as embryos which carry a chromosome abnormality usually do not implant or have a greater chance of resulting in miscarriage.
3. Using the FISH technique, embryos will be tested for chromosomes X and Y, and 13,18 and 21(this testing will detect approximately 80% of major chromosomal aneuploidies or abnormalities). If no abnormality is detected in the embryo(s), further testing of chromosomes 16 and 22 can be performed (this testing will detect approximately another 8-10 % of major chromosomal abnormalities).
4. Patients over 37 years of age who specifically request the procedure.
5. PGD is not offered for sex selection.
6. It is possible that a couple may not have any ambryos for transfer after PGD has been performed, as all the embryos could carry the abnormality or the embryos fail to continue to grow in culture for the extended period before uterine transfer.

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