Preimplantation Genetic Diagnosis (PGD)
PGD is the use of genetic testing technology to evaluate the embryos for chromosome or genetic abnormalities. There are different reasons why PGD may be performed. There are also different techniques that are available for the genetic evaluation of embryos. During the PGD process, eggs and sperm are united through in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI). A cell biopsy is taken from each embryo and sent for genetic analysis. The genetic analysis tells the embryology lab which embryos are genetically normal. Genetically normal embryos have a very high chance of making a pregnancy. California IVF: Davis Fertility Center, Inc. is a leading center in the Northern California and Sacramento area. We have been performing genetic testing procedures since 2005 and our testing volume continues to grow at a rapid rate.
The name "Preimplantation Genetic Diagnosis" is a form of genetic screening. A more correct name for this testing is Preimplantation Genetic Screening, or PGS. The names are often used interchangeably throughout this site.
Reasons for using PGD
Embryos can be analyzed for one or more of the following reasons:
- Aneuploidy - A condition in which there is an extra or missing chromosome. An example of aneuploidy is Down Syndrome. There is an increased incidence of aneuploidy as women age.
- Gender Selection -The determination of whether an embryo is male or female. This is a very accurate way for patients to have a boy or a girl through family balancing.
- Translocations - A change in chromosome structure in which chromosomes are attached to each other or pieces of different chromosomes have been interchanged.
- Single Gene Disorders - Disorders or diseases caused by the inheritance of a single mutated gene. Diseases such as Cystic Fibrosis, Tay Sachs, Alpha and Beta Thalassemia and Sickle Cell Anemia are examples of a mutated gene.
- Recurrent Pregnancy Loss - Genetic testing of embryos can look for genetic causes to repeated pregnancy losses.
- IVF Treatment Failure - one of the most common reasons why IVF doesn't work is related to genetic abmormalities within the embryos.
Advanced Age & Aneuploidy
As a woman's eggs age, the risk of chromosome and genetic abnormalities increases drastically. This causes a lower chance of pregnancy and a higher chance of a miscarriage. It has been known for many years that as a woman ages, her eggs are more prone to genetic errors. These genetic errors will cause the embryos to become genetically abnormal. Most genetically abnormal embryos do not make a pregnancy. Abnormal embryos that do make a pregnancy may result in a miscarriage or a baby with a chromosome disorder such as trisomy 21, or Down Syndrome. Blood testing in pregnancy (MSAFP or triple and quad marker screening) has been used along with ultrasounds and amniocentesis (drawing out fluid from around the baby) to test for chromosome problems during early pregnancy. Preimplantation testing allows for screening of genetic problems before the embryo is placed in the uterus. This avoids a pregnancy with a genetic problem which will drastically increase pregnancy rates and reduce miscarriage rates. Abnormal embryos are not used when PGD or PGS (FISH or CGH) is used.
Help having a boy or girl is now within reach of many couples. When a couple has a boy or girl already and would like to add to their family without having multiple children in order to have the desired sex, genetic screening can help. The X and Y chromosomes determine if you will have a boy or girl. By testing the chromosomes of the embryo, we can know if you will have a boy or girl before you become pregnant. This allows couples to balance their family by using gender selection. While the use of technology for this purpose is not acceptable to everyone, the technology is available to those who find family balancing desirable.
Translocations (unbalanced translocations & Robertsonian translocations)
Translocations are genetic abnormalities where the genetic material from one chromosome has relocated to another chromosome. The person with the abnormality possess all of the genetic material they need but the genes are not in the normal places. A problem arises when the genetic material is passed on to the embryo. Missing or extra genetic information can be passed along. This leads to genetic abnormalities or birth defects. Preimplantation genetic diagnosis can determine which embryos do not show evidence of the translocation. This helps avoid miscarriages and increases the chances of a healthy baby.
Single Gene Disorders
There is a wide range of genetic diseases that can be evaluated using the genetic testing techniques. Current technology doesn't offer a cost effective way to screen for all of the disorders at once. It is more effective to screen for a genetic disorder that is known within the family. Testing for single gene disorders is more complicated than the other tests and often has higher costs. A blood sample may be needed in advance so that the genetics center can create a probe to identify the genetic abnormality within the embryos tested. More information will be provided to you during your consultation if you desire single gene testing. The following is a list of disorders that can be tested. This is only a sample list and many more diseases are add all the time thanks to ongoing research.
alpha 1 anti-trypsin
Becker muscular dystrophy
breast cancer, gene 1 & 2
carbamoyl phosphate synthetase deficiency
central core disease
cerebral arteriopathy (Cadasil)
Charcot-Marie-Tooth syndrome 1A & 1B
chronic granulomatosis disease (CGD)
congenital adrenal hyperplasia
congenital disorder of glycosylation
congenital nephrotic syndrome
Crigler-Najjar syndrome I
Duchenne muscular dystrophy
early onset Alzheimer disease
early onset torsion dystonia
Emery Dreifuss muscular dystrophy
epidermolysis bullosa, dominant dystrophic
- Herlitz junctional, gene 1 or gene 2
epidermolytic palmoplantar keratosis
facioscapulohumeral muscular dystrophy
familial adenomatous polyposis
familial amytrophic lateral sclerosis
(Lou Gehrig's disease)
Recurrent Pregnancy Loss (RPL) is defined as the occurrence of three or more consecutive losses of clinically recognized pregnancies prior to the 20th week of gestation (ectopic and molar pregnancies are not included). Evaluation of healthy women is not recommended after a single first trimester or early second trimester spontaneous miscarriage as these are relatively common, sporadic events. The risk of another pregnancy loss after two consecutive miscarriages is 24 to 29 percent, therefore, evaluation and treatment of RPL can reasonably be started after two consecutive miscarriages. Many doctors may advise their patients to wait until three losses to start a diagnostic evaluation. In many cases, there is not an identified cause for recurrent pregnancy losses. A very high percentage of pregnancy losses occur because of genetic or chromosome abnormalities occurring in the embryos. Some women have predisposing factors that cause them to have genetically abnormal embryos at a higher rate than other women even though she has a normal chromosome analysis herself.
Preimplantation genetic screening for aneuploidy (chromosome number) can avoid most miscarriages to to abnormalities due to missing or extra chromosomes. PGD / PGS will not affect pregnancy losses caused by other problems such as fibroids, blood clotting disorders, and antibodies such as antiphospholipid antibodies and anticardiolipin antibodies. (APA, LAC, ACA). Women with multiple pregnancy losses may wish to consider genetic screening of their embryos. This option can be discussed along with other topics concerning recurrent pregnancy losses during a consultation with on of our doctors.
One of the most common causes for a failed IVF cycle is the absence of genetically normal embryos. While many other factors may also affect the success of an in vitro fertilization treatment (IVF), genetically abnormal embryos is a leading cause of IVF not working. Laboratory culture conditions used to grow embryos to the more advanced stage and uterine abnormalities are the other leading causes of IVF failure. When IVF doesn't work, many problems are blamed for the lack of success. Many labs and clinics have adjusted many variables in order to increase the chances of having a positive pregnancy test and healthy baby. It is very surprising to find how many embryos are genetically abnormal. Women may have factors affecting their ovaries that cause them to make genetically abnormal embryos at a much higher rate that expected. This leads to an unsuccessful IVF treatment. At California IVF: Davis Fertility Center, Inc., our success with donor eggs, frozen embryos, and pre implantation genetic screening (PGS & PGD) stands as a testament to the high quality laboratory and embryology services. We will be happy to discuss your options for improving your outcome with genetic testing. It must be understood that the testing will not make the embryos normal and in some cases, we will not recommend genetic testing if it will not likely improve your chances of having a baby.
Genetic testing of embryos is not likely to help a woman who goes through IVF treatments and has a low number of eggs that results in only a few embryos available for transfer. If all of the available embryos were put into the uterus, a normal embryo would have been put into the uterus if there was one present. Genetic testing is useful for avoiding the situation where the good embryos are placed into cryo storage. The freezing and thawing may affect the success of future attempts using the frozen embryos. A program with a high success rate using frozen embryos can rival the chances of genetically tested embryos, but multiple transfers may be necessary. Patients must also consider the cost of the genetic testing. The advantages and disadvantages of genetic testing can be discussed at your consultation with one of our doctors.
Preimplantation Genetic Diagnosis (PGD) Techniques
The most commonly used techniques for PGD include FISH and CGH . Information on the technical aspects of preimplantation genetic diagnosis can be found here. This link will review the various types of PGD and PGS including CGH and FISH technology.
In early 2010, California IVF: Davis Fertility Center, Inc., announced a cooperative effort with Gene Security Network to offer Sacramento area and Northern California region patients the option of combining 24 chromosome analysis with screening for single gene disorders. This now gives us the ability to avoid a known inherited disease that exists in a patients family at the same time we test for the presence of the 23 pairs of chromosomes. We remain committed to bringing our patients the latest developments to improve the chances of having a safe pregnancy and a healthy baby.
If you have any questions about our services or the use of preimplantation genetic diagnosis (PGG) with your fertility treatments, or to screen for an inherited genetic disorder, please contat our office. We are always happy to answer your questions.