Pre-implantation Genetic Diagnosis (PGD) is a procedure in which embryos created through in-vitro fertilization (IVF) can be tested for genetic problems prior to being placed into the uterus to establish a pregnancy. This technology has existed for over 15 years but it has only recently become readily available to a wide variety of patients. With the increased emphasis on screening potential parents to see if they are carriers for genetic disease, PGD has become an excellent option for patients who test positive and wish to avoid having a child with a specific genetic disorder.
The technique of PGD requires undergoing an IVF cycle in which the woman takes fertility medications to make multiple eggs grow. Frequent ultrasounds and blood tests are necessary to monitor the progress of egg development. Using ultrasound guidance under gentle anesthesia, a needle is placed through the vaginal wall into the ovaries to retrieve the eggs. These eggs are then fertilized with the male partner’s sperm by injecting a single sperm into each egg with a procedure called intracytoplasmic sperm injection (ICSI). After fertilization, the fertilized eggs, now called embryos, grow for 3 days in an incubator in the IVF lab. At this point the embryos contain 6 to 8 cells and one or two cells can be removed with a procedure called embryo biopsy without permanently damaging the embryo in most cases. These cells can then be screened to determine if that embryo carries the genetic problem that the couple wishes to avoid. Since there are multiple embryos to choose from, only the embryos without the genetic problem are placed back into the uterus to attempt to establish a pregnancy. The abnormal embryos are discarded. Since only 2-3 embryos are usually transferred back to the uterus, extra normal embryos can be frozen for later use. Success rates are generally good (around 50% per try) because most patients undergoing PGD are not infertile; however, many factors such as the age of the woman and the quality of the sperm can affect the chance of success.
PGD has been applied to a wide variety of genetic disorders including diseases caused by an abnormality in a single gene and for diseases caused by abnormalities in the structure or number of chromosomes. Examples of common single gene disorders include cystic fibrosis, Tay Sachs disease and sickle cell anemia. Examples of chromosomal abnormalities include translocations, inversion and deletions of pieces of the chromosomes. Patients with recurrent miscarriages due to chromosomal abnormalities can have PGD done to avoid replacing embryos with an unbalanced genetic make-up, thereby lowering their risk of miscarriage. PGD offers patients who are at risk of having a child with a genetic disease the opportunity to reduce this risk by screening the embryos before pregnancy. If you are interested in learning more about this technology, please call our office to set up a consultation.