Preimplantation Genetic Diagnosis & Screening
At Yale, it is possible to increase the chance of successful pregnancy through techniques known as PGD (Preimplantation Genetic Diagnosis) and PGS (Preimplantation Genetic Screening). Both techniques involve the biopsy of an embryo to remove 1 cell if performed on day 3 or multiple cells if performed on day 5.
- What is PGD?
PGD is process by which embryos are screened for specific genetic defects in embryos before transferring them into the uterus. Following the genetic analysis of the biopsied cell, your physician will have valuable information to aid in the decision about which embryo(s) to transfer.collapse
- What is PGS?
- PGS is a process by which embryos are screened for chromosomal abnormalities before transferring them into the uterus. This testing uses similar techniques to those used in PGD, but screens for chromosomal abnormalities rather than looking for a specific disease. This technology is used to select chromosomally normal embryos for transfer.collapse
- What types of Genetic Defects can be identified with PGD?
- Monogenic (single gene) disorders: these are diseases caused by mutations in specific genes. PGD can be used to avoid the risk of transmitting a genetic disease, such as cystic fibrosis, thalassemia, hemophilia, muscular dystrophy, etc. when one or both parents are carriers of a disease-causing mutation that could be transferred to offspring.
- Chromosomal rearrangement: PGD can be used to avoid the risk of transmitting a chromosomal defect, such as unbalanced translocation, inversion, or deletion when one of the parents carries a balanced chromosomal defect.
- What types of Genetic Defects can be identified with PGS?
- Aneuploidy: this is a condition characterized by an abnormal number of chromosomes in the offspring. Lack or surplus of an additional chromosome always leads to birth defects, the severity of which depends on the affected chromosome. The vast majority of miscarriages are due to aneuploidy of a chromosome that is incompatible with life. The most common aneuploidies among live births are trisomies (3 instead of 2 chromosomes) of chromosomes 21, 18, and 13, and monosomy (1 instead of 2 chromosomes) of chromosome X.collapse
- Who is at risk for aneuploidy?
- Advanced maternal age: It is known that women approaching 40 are at a higher risk of having a baby with a chromosome abnormality (most notably Down's syndrome). With PGS, embryos are tested for chromosome defects before being transferred into the uterus.
- Multiple IVF failures: Failure to achieve a pregnancy after multiple cycles of IVF with embryo transfer can leave couples in a distressed state. PGS may help explain IVF failure.
- Recurrent spontaneous miscarriages: To reduce the risk of recurrent spontaneous abortions or miscarriage in couples that had 2 or more pregnancy losses due to aneuploidy of the fetus. Recurrent miscarriage is also common in couples where one or both are carriers of chromosomal defects (balanced translocations).
- Is In Vitro Fertilization (IVF) required for PGD/PGS?
In order to perform PGD/PGS testing, the embryos must be accessible, and thus, In Vitro Fertilization (IVF) is required. PGD/PGS is offered to both fertile and infertile couples.collapse
- What happens during PGD/PGS?
- During the process, one single cell (blastomere) from a 4-8 cell embryo is removed and analyzed. At this stage, all cells of an embryo are equal and capable to give rise to all organs of the future person, and generally there is no damage to the embryo by removing one cell. Alternatively, a group of cells from an embryo reaching the blastocyst stage (after 5 days in culture) can be biopsied and tested.collapse
- Where is the preimplantation embryo kept during testing?
- While the testing takes the embryo is developing in the laboratory. This is a standard procedure for all IVF embryos, independent of PGD/PGS. After 5-6 days development in the lab, the embryos can either be transferred to the uterus for implantation, or frozen and transferred in a future cycle. Recent advances in freezing procedures, available at Yale, ensure freezing without any viability compromise.collapse
- Who performs the embryo biopsy?
Our expert embryologists have been trained extensively to perform embryo biopsy.collapse
- Who performs the testing of the biopsied cell(s)?
In the recent years, PGD/PGS was revolutionized by the development of methods that are extremely accurate and efficient in testing specific gene mutations and aneuploidy from a single or very few cells. These procedures allow us to examine whether an embryo has the correct number of chromosomes or carry a disease-causing mutation. For example, they help detect embryos that have a high chance of carrying an extra chromosome 21 (Down's syndrome) or other common chromosomal problems that could lead to miscarriage.
Depending on the indication, the cells biopsied at Yale are sent to one of the following PGD providers, all offering state-of-the art testing:collapse
- What happens if there are several normal embryos?
The additional normal embryos can be frozen to be used to achieve a future pregnancy. Therefore, there will be no need for another IVF-PGD cycle if there are several normal embryos obtained in one cycle.collapse
- How can I arrange for a consultation?
Please call our New Haven or Westport offices to arrange a consultation with one of our expert physicians. Make sure you mention that you interested in learning more about PGD/PGS. You are kindly requested to bring any Molecular Genetics Diagnosis documents you may possess to your first appointment. Such documents, if available, will help our physicians start the process. Don’t worry if you don’t have any of these records. We will arrange all of the necessary testing after your initial consultation.collapse