Preimplantation Genetic Diagnosis Process
IHR provides highly successful IVF with PGD treatment.
Preimplantation genetic diagnosis (PGD) is an advanced genetic test performed before pregnancy. Embryos obtained by IVF are tested for chromosomal abnormalities or a known genetic mutation. Only the unaffected ones are transferred into the uterus for the woman to conceive with a healthy baby. PGD has been successfully applied at IHR as a clinical service for over 10 years now for many different genetic diseases resulting in hundreds of healthy children born.
IHR collaborate with the Reproductive Genetic Institute, a word known Chicago based PGD laboratory. We can offer PGD by sampling the first and second polar bodies, single blastomere biopsy from a 3-days old embryo, or by trophectoderm biopsy (cells that will develop to be the placenta and not from the embryo – like a very early CVS) from embryos that developed to blastocysts (day5-6 embryos with 70-80 cells). The first polar body is discarded from the egg during oocyte maturation, prior to fertilization and contains one set of duplicated chromosomes (with two chromatids in each chromosome), while the second polar body is discarded from the egg after fertilization and contains one set of chromatids. By testing the first and second polar bodies for a female carrier of a specific genetic disease, the geneticists can determine whether the woman's eggs carry the abnormal gene or not. The procedure is offered to couples that the female partner is a known carrier of genetic diseases (such as Fragile X syndrome). DNA analysis by PCR will confirm the diagnosis. IHR physicians have already performed over 1000 IVF with PGD treatment cycles involving preimplantation diagnosis for cystic fibrosis, thalassemia, Tay-Sachs disease, sickle cell disease, and other diseases. IHR's expertise in preimplantation genetic diagnosis lies in our willingness and ability to individualize our approach to best suit each and every one of our patients. If you have any questions as you review the material on preimplantation genetic diagnosis, please contact us for a FREE Preimplantation Genetic Diagnosis E-Mail Consultation.
Chromosome abnormalities (aneuploidies) are associated with failed implantation, pregnancy loss, and the birth of children with multiple congenital anomalies. Preimplantation genetic diagnosis (PGD) provides a means of testing for these chromosome abnormalities and selecting the best embryos for transfer. Embryos with chromosome abnormalities are physically indistinguishable from healthy embryos; therefore, without PGD, abnormal embryos are equally likely to be transferred, reducing the chances of achieving a viable and healthy pregnancy.
Prior aneuploidy testing involved analysis of a single cell by fluorescence in situ hybridization (FISH), using probes for a limited number of chromosomes. FISH testing is able to detect the most common chromosome abnormalities, including Down syndrome, Trisomy 18, Trisomy 13, and sex chromosome anomalies, in order to reduce the risk of having an affected pregnancy or child.
Research shows, however, that abnormalities involving any chromosome can increase the risk of miscarriage and reduce the effectiveness of IVF. IHR’s new 24-chromosome testing is able to analyze the entire chromosome complement of a single cell, reducing the risk of failed implantation and miscarriage, and increasing the chance of having a healthy baby. Recent prospective randomized trials showed that when embryos are biopsied at the blastocyst stage (day 5-6) and tested by PGS for 24 chromosomes embryo implantation and delivery rates improved significantly.
IHR offer 24-chromsome analyses using a technique called microarray, or array comparative genome hybridization (a-CGH). This technique compares the amount of DNA present for each chromosome in a single cell, and compares it to that of a normal standard. Microarray can be performed on three different sample types: polar bodies (from fertilized eggs), blastomere (from Day 3 embryos), or trophectoderm cells from a blastocyst/Day 5-6 embryos). Embryo transfer during the same cycle is feasible for polar body and/or blastomere testing, whereas trophectoderm testing typically requires embryo freezing and thawing for transfer at a later date. With today freezing technology, outcome of frozen-thawed embryo transfer is as good or even better than of fresh transfer. Results are concise and reliable, and the genetic counselors are available to provide clear interpretation of the data.
It is important to remember that like in any test in medicine, misdiagnosis may unfortunately occur. The error rate of PGD is nevertheless very low and is at less than 1%. During the genetic consultation about PGD that each patient will undergo, the specific strategy for the PGD test for this couple will be discussed, including possible rare risks and complication, and the limitations of the techniques. The IVF doctor will consult you on the IVF process, and possible risks and complications of the ovarian stimulation, medications used, procedures, multiple pregnancy, and outcome. The experience of the IVF doctor and center with patients coming for IVF because of PGD may affect the outcome. Biopsy for PGD, especially if performed at experienced centers, of the polar bodies (small particles with the genetic mirror image of the egg) or trophectoderm biopsy on day 5-6 at the blastocyst stage (embryo with 70-80 cells), seems to have no significant short-term or long-term impact and may be used safely for embryo biopsy without notably reducing the pregnancy and delivery rate. Biopsy on day 3 embryos (6-8 cells) is now consider less optimal and usually would be ordered by IHR physicians for specific indication (such as confirmation of inconclusive polar bodies’ results or for translocation testing with conversion to distinguish between normal and balanced embryo).
The other important application of the polar body testing is preimplantation screening (PGS) of Down syndrome and other common aneuploidies, for couples that wish to avoid any embryo manipulation. Many patients referred to In Vitro Fertilization program (IVF) are of advanced maternal age (35 years of age or older at the time of delivery), which places them at elevated risk for conceiving a child with an extra chromosome and thus delivering a child with Down syndrome (extra chromosome 21) or other common trisomies (Trisomy 13 and 18). Aneuploidies may also result in spontaneous abortions (miscarriage) or nonimplantation, decreasing considerably the chances of the patient achieving a pregnancy. Therefore, by testing for the conditions beforehand, we can prevent these events. Since > 90% of embryo trisomies are originated from the egg (oocyte myotic errors), Polar body testing by FISH or for 24 chromosomes may provide significant assurance for such couples. Polar body removal involves the removal of the first and second polar bodies and analysis of the chromosome number in both the first and second polar body by FISH or aCGH. Only embryos resulting from the fertilization of eggs with normal number of the chromosomes are transferred or frozen. Polar body testing can not provide information of the gender of the embryo since the male contribution can not be analysed.
We also offer Preimplantation diagnosis based on blastomere biopsy. The most common application of blastomere biopsy is preimplantation sexing by FISH to avoid the pregnancy with X-linked disorders, such as hemophilia A and muscular dystrophy, or for single gene disorders in which the male partner is affected.
IHR has treatments for a variety of conditions, including unexplained infertility, ovulatory dysfunctions, endometriosis, immunological infertility and many others. Perhaps less known is our work with individuals and couples who are considering assisted reproduction, but who are uncertain of their next step. We encourage anyone, before they make a decision, to consult with us. Currently, we are offering a FREE Preimplantation Genetic Diagnosis E-Mail Consultation.