Frequently Asked Questions Regarding Preimplantation Genetic Diagnosis and Screening
Preimplantation Genetic Diagnosis, or PGD, is a specialized laboratory test which screens embryos for specific genetic diseases and chromosome abnormalities using a single cell. Only embryos found to be free of both are transferred to the mother's womb, reducing the possibility of genetic disease or chromosome abnormality. A couple's chance of becoming pregnant may also increase, and the chance of miscarriage decrease, in an IVF cycle where PGD is used to test for chromosome abnormalities.
Chromosomes are structures in the body comprised of thousands of genes. A healthy baby has 46 chromosomes in each cell of their body. “Chromosome abnormality” refers to an atypical number of chromosomes and is generally caused by an error in cell division in either the egg or sperm or in the first few days of embryo development. Embryos with chromosome abnormalities are less likely to implant and more likely to end in miscarriage. Most babies born with chromosome abnormalities will have mental retardation and/or birth defects. An example of a common chromosome abnormality is Down Syndrome.
PGD is performed on a single or few cells extracted from a the embryo, without impacting the development of the embryo, using a medical laser which creates a hole in the zona pelucida, the membrane “shell” of the embryo. The embryo is immediately returned to culture until the testing is complete and embryo transfer can take place. It is upon this single or few cells that the PGD is performed. Only embryos that continue to develop and show no abnormality following PGD (depending on the type of PGD) are suitable for transfer.
CGH is the most comprehensive and accurate testing technology available to screen all 23 pair of chromosomes in a single embryo cell. This process has been shown to be highly accurate across all chromosomes, including the sex chromosomes, and provides more information than other testing technologies.
Patients with a variety of medical histories achieve pregnancy following PGD . Studies published using other testing technologies suggest that PGD may be most beneficial in patients who are 35 years of age or older (mothers), have a history of recurrent pregnancy loss, or have experienced previous IVF implantation failure. Patients also choose testing to reduce the chance of conceiving a child with a chromosome abnormality like Down Syndrome.
A number of factors are considered in determining whether an embryo is transferred including:
- Embryo morphology (do they develop well enough to transfer)
- Aneuploidy rate (influenced by maternal age and medical history)
- Number of embryos tested
Women aged 35 or younger who have eight or more embryos tested have a 99% chance of having one or more embryos to transfer. In women aged 36 and older this chance decreased to 75%. These numbers will be lower if less than eight embryos are tested or if maternal age is 40 years or older.
The rate of aneuploidy does increase as women get older. However, aneuploidy is still common in embryos regardless of the age of the mother.
Reprogene feels it is important for patients to be well informed about genetic testing. For this reason we have a number of Genetic Counselors on staff who have special educational training in genetics. A Genetic Counselor is available to speak with you by phone regarding the risks, benefits, and limitations of PGD and testing with Parental Support. This free service is available regardless of whether you proceed with testing or not. Reprogene strongly encourages the use of this service and appointments can be made by calling our office at any point following receipt of a testing referral by your doctor.
1) Your doctor completes a testing referral.
2) You will then begin your IVF cycle at your IVF center.
3) After Egg Retrieval, the embryologist at your IVF lab will perform an embryo biopsy to remove a single or few cells from each embryo. These cells will be prepared according to Reprogene's careful instructions and shipped to Reprogene's laboratory. Only a single or few cells from each embryo will be shipped to the Reprogene laboratory; the embryos themselves will remain at your IVF clinic until your embryo transfer.
4) Reprogene will test the cells and return the results to your doctor who will use the information to determine which embryos to transfer and/or cryopreserve.
If your IVF clinic currently offers PGD, all you need to do is ask your doctor to submit a testing referral request to Reprogene.
If you have not already started your egg retrieval, there is no charge.
All information that we communicate with you or with your physicians will be done in accordance with HIPAA regulations.
Simply contact Reprogene directly or let your doctor know that you wish to consider PGD testing for your IVF cycle.