In Vitro Fertilization
PGD
What is PGD?
PGD is a technique used during in vitro fertilization procedures to test the embryos for genetic or chromosomal disorders prior to transfer into the uterus.
This testing may prevent the transmission of certain heritable genetic and chromosomal disorders.
By contrast PGS (preimplantation genetic screening) is the evaluation of embryos for multiple abnormalities at once. The purpose of PGS is to increase the chance of a live birth, not to diagnose known diseases. PGS will be discussed separately below.
Who is a candidate for PGD?
PGD is indicated for couples who are known to be carriers for a specific genetic disorder. Disorders successfully prevented by PGD include: cystic fibrosis, Huntington’s disease, sickle cell disease, BRCA1 mutations (a cancer causing gene), Tay Sachs, Fragile X, myotonic dystrophy, and others. Some couples also want PGD for family balancing, to increase the chance that they will conceive a girl or a boy.
How is PGD performed?
To accomplish PGD, embryos are obtained through an IVF cycle. One to two cells are biopsied from the embryo, and are evaluated. A diagnosis is obtained within a day of the test; only unaffected embryos are replaced into the uterus.
The two most common lab techniques utilized during a PGD cycle are fluorescent in situ hybridization (FISH) and polymerase chain reaction (PCR). FISH is utilized to study chromosome numbers, and in some cases, structure. PCR is used to detect single gene (monogenic) disorders. DNA from the embryo is studied to determine the presence or absence of the mutation.
What are the risks of PGD?
The goal of PGD is the birth of an unaffected, healthy child. However, no technology is perfect. It is possible that embryos could be damaged by the PGD biopsy. If these embryos stop growing, it’s difficult to know how they may have faired if no biopsy had been performed. The PGD procedure itself has not been linked to any birth defects.
In some cases embryos can be misdiagnosed. Specifically, when testing for specific gene disorders, the chance of transferring an affected embryo that was mistakenly identified as normal is between 2% and 11% depending on the specific disorder being tested for.
What are the costs of PGD?
PGD adds additional cost to the IVF procedure. The biopsy of embryos costs $tktk and the diagnostic testing runs $tktk. Other incidental costs for embryo shipping may be incurred.
What is PGS?
Preimplantation genetic screening (PGS) is the testing of embryos for multiple genetic disorders at the same time. PGS is performed on embryos of parents with no known genetic defects. The premise behind PGS is that we might be able to increase the chance of a live birth if we screened all embryos for major chromosomal abnormalities such as Down Syndrome. Several techniques have been tried including FISH and a technique called CGH (comparative genomic hybridization.)
While PGS sounds promising, to date it has failed to deliver in its efforts to improve live births rates or the health of offspring. We think it is best to follow the American Society of Reproductive Medicine’s Practice Committee Opinion: “A careful review of the published studies of this technique led the ASRM Practice Committee to conclude that the available evidence does not support the use of PGS to improve live-birth rates in patients with advanced maternal age, previous implantation failure, recurrent pregnancy loss, or to reduce miscarriage rate in patients with recurrent pregnancy loss related to aneuploidy at this time.” ASRM Press Release, Tuesday, October 16, 2007.
Since the release of that opinion, no further studies have been published which would change our perspective on PGS. We will remain vigilant in monitoring the progress of PGS. If the techniques improve to a point where patients receive the benefit of the additional costs, we would feel justified in offering it.