Aneuploidy (Chromosome) Screening
About PGD for Aneuploidy
Aneuploidy is a term used to describe a chromosome problem that is caused by an extra or missing chromosome. The most commonly known example of aneuploidy is Down syndrome, which is caused by an extra copy of chromosome 21.
Chromosomes are the structures in our cells that carry our genetic information (genes). Typically, we have 46 chromosomes in each of our cells. The chromosomes come in pairs (23 pairs in total); one copy of each chromosome is inherited from the egg, and the other copy is inherited from the sperm. Cells/embryos with 46 chromosomes are called euploid (correct chromosome number). If an egg or sperm is missing a chromosome or has an extra chromosome , this situation is referred to as aneuploid (incorrect chromosome number).
How can PGD for aneuploidy help my family?
PGD is currently the only way to determine if an egg or embryo contains an abnormal number of chromosomes prior to pregnancy. This reduces the chance of having a child with a chromosome abnormality (which often causes birth defects and cognitive disabilities), and increases the efficiency of IVF. PGD for aneuploidy increases the chance of an embryo implanting and decreases the chance of miscarriage, thereby increasing the chances of having a successful pregnancy and healthy baby.
Without PGD, embryos are selected for transfer based on their morphology (physical appearance and development). It is important to note, however, that an embryo’s development is not always associated with its chromosomal content. Therefore, a well-developed embryo may be selected for transfer, but may not result in a pregnancy due to abnormal chromosomes. PGD can give your physician another way to select the best embryos for transfer, in order to maximize the chances of having a successful IVF cycle.
What is my risk for aneuploidy?
Every couple will produce a proportion of embryos with chromosome abnormalities. This proportion increases as a woman gets older. The risk for aneuploidy is independent of medical or family history and ethnicity.
Since most embryos with chromosome abnormalities will fail to implant or will result in miscarriage, the frequency of aneuploidy in IVF embryos is much higher than the number of babies born with chromosome abnormalities. For example, a 40-year-old woman has approximately a 1 in 66 (1.5%) risk of having a liveborn child with a chromosome problem. At the time of IVF for a 40-year-old woman, approximately 60% of embryos will be abnormal, the majority of which would result in failed implantation or miscarriage.
It is well known that the pregnancy rate after IVF decreases dramatically with maternal age. Aneuploid embryos have a lower survival rate than normal embryos, and the majority fail to implant. Therefore, the decrease in pregnancy rates with maternal age is partly caused by the increase in aneuploid embryos. By testing embryos for aneuploidy and selecting for embryos with normal chromosomes, pregnancy rates noticeably increase.
How does RGI test for aneuploidy?
Aneuploidy testing can be performed by two possible methods:
RGI-CompleteTM Array Comparative Genomic Hybridization (Array CGH or aCGH)
Array CGH allows the laboratory to determine if the correct number of all 24 chromosomes (1-22, X and Y) are present in the egg or embryo. This state-of-the-art technology has shown the most promise in enhancing the effectiveness of IVF. With array CGH, the amount of DNA present for each chromosome is compared to that of a normal standard, enabling us to detect missing or extra chromosomes.
This method of testing can be performed on polar bodies (by-products from the egg), blastomeres (cells from the Day 3 cleavage stage embryo), or trophectoderm (cells from the Day 5/6 blastocyst). RGI strongly encourages that this testing be performed on blastocyst samples, due to increased accuracy and better test performance.
Read more about RGI-CompleteTM 24-Chromosome testing.
Fluorescence In Situ Hybridization (F.I.S.H.)
F.I.S.H. is a technology that allows our laboratory to determine the presence or absence of particular chromosomes. Probes labeled with fluorescent signals are used to identify specific chromosomes, and can be used to count the number of these specific chromosomes in a cell from an egg or embryo.
RGI offers different options for common chromosome testing by F.I.S.H.:
- Five chromosomes
- Chromosomes 13, 18, 21, X and Y
- Chromosomes 13, 16, 18, 21, 22
- Eleven chromosomes
- Chromosomes 8, 9, 13, 15, 16, 17, 18, 21, 22, X, Y
Why do we test for these particular chromosomes?
- Chromosome 21: causes Down syndrome
- Chromosome 13, 18: cause Trisomy 13 or Trisomy 18, in which babies usually do not survive for more than a few months of life
- Chromosome X, Y: cause abnormalities such as Turner syndrome, which is a common cause of miscarriage or can result in birth defects and later infertility
- Chromosomes 16, 22: common causes of miscarriage
- Chromosomes 8, 9, 15, 17: cause failed implantation and miscarriage
F.I.S.H. analysis is typically performed on polar bodies (by-products from the egg) or blastomeres (cells from the Day 3 cleavage stage embryo).
What is the accuracy of the testing?
The accuracy of PGD for aneuploidy ranges from approximately 90-98%, depending on the stage at which the embryo is sampled. Our genetic counselors are happy to discuss the benefits and disadvantages of different sample types with you.
Is there a waiting period? Do I need to submit a blood sample?
No. RGI’s aneuploidy testing does not require a waiting period, and does not require the submission of blood samples. As well, there is no penalty if testing is canceled.
Informational Resources and Next Steps
Please review our PGD brochures for 24-chromosome testing or common chromosome testing and our general information packet for aneuploidy, and contact our genetic counselors via email or at 773-472-4900 to schedule an appointment or to discuss next steps.