The latest in IVF technology is now available at CNY Fertility Center through Reprogenetics! If you’re interested in PGD or would like more information, contact us at 800.539.9870 (toll free) or ask us about it during your consultation.
What Does PGD Have To Do With Becoming (and staying) Pregnant?
By now, you may have heard the term PGD. It stands for Preimplantation Genetic Diagnosis, an advanced genetics test used in conjunction with in vitro fertilization to determine the status of an embryo’s chromosomes.
Our physicians are being asked with greater frequency about PGD. It’s easy to understand why: recent studies show that PGD may improve a woman’s chance of getting pregnant and carrying that child to term. It can also significantly reduce the chance of a baby being born with an atypical number of chromosomes.
How can PGD help improve my chances of becoming pregnant or carrying to term? Studies reveal that PGD of aneuploidy increases the chance of implantation (1,2), reduces pregnancy loss (3,4), and increases live births (4). Data from Reprogenetics, the leader in PGD, cites a four-fold reduction in the frequency of chromosomally atypical conceptions after PGD (3).
How does PGD work?
An IVF embryologist carries out the process by removing a cell or blastomere from the embryo on the third day of its development through the use of microsurgical techniques and fixing the cell on a glass slide. Each cell is usually representative of all cells from that particular embryo. At a specialized genetics center like Reprogenetics, geneticists use a technique called FISH (fluorescence in situ hybridization) to identify the chromosomal makeup of the cell and determine which embryos are the most suitable for replacement in the woman’s uterus. In the meantime, during PGD, the embryos develop undisturbed in an incubator.
In some cases polar bodies, two small cells produced by the ripening egg before fertilization, may be tested. This only provides genetic information from the egg. It will not detect abnormalities that may occur once the egg is fertilized by sperm.
Is PGD 100% accurate?
PGD, the only test available to determine aneuploidy, has an accuracy rate of over 90%. Reprogenetics latest tests show a false positive error rate of only 4.7% (5). Yet, to identify a false negative (classifying an abnormal embryo as normal), prenatal testing is still recommended via chorionic villous samples (CVS) or amniocentesis.
Are there risks to the embryo?
PGD apparently has no affect on normal development of the embryo or fetus. It is estimated that the removal of one cell reduces the ability of the embryo to implant by less than 3%.
What patients stand to benefit from PGD?
Virtually all couples over 35 without a history of repeated IVF failures are excellent candidates. Studies show that women who have Recurrent Pregnancy Loss (6), previous aneuploid conceptions (7), known chromosome abnormalities and single gene defects, can also benefit. It is not clear if women with repeated IVF failures would be good candidates for the procedure (2). In any of these problems, men as well as women may be the cause of the failure.
What is the cost for PGD?
There is an additional cost for PGD, above that of your IVF cycle. In addition to the removal of the cells from the embryo, a procedure performed at the IVF center, actual testing is done at a specialized laboratory. Insurance may cover PGD. For more information contact our financial coordinator.
If I am interested in PGD, how should I proceed?
Speak to your Doctor, Nurse or anyone you see at your consult and they will answer any questions you may have and assist you in proceeding.
What should I know about chromosomes?
If you look at a cell under a microscope, you’ll see string-like structures in the cell’s center, or nucleus. These are chromosomes, which contain DNA – our genetic roadmap. Normal human cells (for adults, babies, fetuses and embryos) contain 46 chromosomes in 23 pairs, half from each parent.
The condition of having an embryo or zygote with either more or less than 46 chromosomes is called aneuploidy. Very often, the likelihood of aneuploidy increases with the age of the woman, but it can also occur in women under 35. Aneuploid embryos may have extra (called trisomy) or missing (monosomy) chromosomes. A baby carrying an extra or missing chromosome may be born with mental and/or physical defects. Down syndrome is a common example.
How does aneuploidy affect my ability to conceive or maintain a pregnancy?
A chromosomal abnormality can prevent the embryo from attaching to the wall of the uterus, eliminating any chance of pregnancy. It may also cause the implanted embryo to stop developing, resulting in a pregnancy loss.
More than 50% of embryos from women who are 35 to 39 show chromosomal abnormalities, while those over 40 have a frequency of aneuploidy of 80% or higher. That’s why the percentage of older women becoming pregnant is so low. Additionally, experts consider aneuploidy to be the biggest factor for Recurrent Pregnancy Loss (or miscarriages) among women 35 and older, responsible at least half the time.
Why is aneuploidy more likely to affect older women?
Since women have eggs that are as old as they are – females have all of their eggs from the fetal stage onwards; they don’t add new ones later on – experts believe that these older eggs are less likely to divide properly. Eventually, this results in similar problems once the egg becomes fertilized.
Key Words to Remember:
Aneuploidy. A condition of having less than or more than the normal number of chromosomes.
Blastomere. A cell that is removed from the embryo for PGD.
Chromosomes. The structures in the cell’s nucleus that contain DNA.
Fluorescence in situ hybridization (FISH). The specialized procedure used to count the chromosomes under a fluorescent microscope.
Monosomy. Condition where a chromosome is missing from the embryo.
Polar Bodies. Two cells produced by a ripening egg before and during fertilization that can be tested to determine the egg’s chromosomes.
Preimplantation Genetic Diagnosis (PGD). The test used to determine chromosomal abnormality during the in vitro process.
Trisomy. Condition where the embryo has an extra chromosome.
Zygote. Fertilized egg or first stage of the embryo.
References:
1. Gianaroli et al 199 Fertil Steril 72:837-844
2. Munne et al 2003 Repro Biomed Online 7:91-97
3. Munne et al 200 Fertil Steril 85:326-332
4. Munne et all 1999 Hum Reprod 14:2191-2199
5. Colls et al Fertil Steril, in press
6. Munne et al 2006 Fertil Steril 85:326-332
7. Munne et al 2004 Prenat Diagn 24:638-647
To do further research on this subject visit these websites:
http://www.emedicine.com/med/topic3520.htm
http://www.dnapolicy.org/
