Pre-Implantation Genetic Screening and Diagnosis

What are the types of PGS/PGD and who should consider?

PGS for chromosomal screening

• Women with infertility related to recurrent miscarriage
• Women with previously unsuccessful IVF cycles
• Women of advanced reproductive age

PGD for chromosomal rearrangements

• Individuals who carry known chromosomal rearrangements such as translocations or inversions

PGD for single gene disorders

• Individuals or couples who carry a gene(s) for a specific genetic disorder (such as cystic fibrosis, spinal muscular atrophy, Tay-Sachs disease, fragile X syndrome, etc)
• Not sure if you’re a carrier of a single gene disorder? NRM is the only clinic in Vermont offering pan-ethnic carrier screening with GoodStart technology called next-generation DNA sequencing (NGS).

What is a “normal” embryo?

One of the hardest decisions in IVF is identifying which embryo(s) to transfer. In the past due to this unknown, multiple embryos (often up to 3-5!) would be transferred in an effort to maximize chances of success, but this increased the risk of multiple pregnancy—often a tremendous risk to the likelihood of pregnancy success and healthy babies. Click here for ASRM Bulletin. In order to choose the best embryo to transfer, we utilize the latest technology to screen chromosomes—PGS—allowing us to learn more about the genetic competency of embryos.

What you need to know about PGS for chromosomal screening:

• Normally, there are 23 pairs of chromosomes in each human cell, for a total of 46 chromosomes. This is referred to as euploidy.
• One pair of each (23 chromosomes) comes from the mother the father.
• Although you and your spouse are likely to be genetically normal, when the egg matures or the embryo develops, errors may occur in the chromosome number of your embryo. This is called aneuploidy and is more common as women age.

Aneuploidy is the most common reason for:

• Failure of pregnancy to occur despite a normal-appearing embryo
• Biochemical pregnancy loss (an initial pregnancy as seen by +bHCG testing which then fails to develop)
• Miscarriage
• Chromosomally affected infant (such as Trisomy 13,18, and 21 “Down’s Syndrome”)

By testing embryos for chromosomal aneuploidy prior to embryo transfer, we improve our ability to select the best embryos for transfer, in an effort to increase your pregnancy rate.

What is the process of PGS/PGD?

If you or your partner carry a known genetic disorder, the first step is to work with your physician and the genetics laboratory to set-up a probe that can detect the gene of concern. If you are undergoing PGS (for screening purposes), the first step is preparing for an IVF cycle.

Following IVF with ICSI, the first step is embryo biopsy. We have highly experienced embryologists who can perform microsurgical removal of one cell from a 3-day old or a few cells from a 5or 6-day old embryo. The biopsied cells are then placed in special containers in dry ice, and sent to a central PGS/PGD laboratory where each sample is analyzed independently.

We prefer to obtain testing cells from the embryo through a blastocyst (day-5) biopsy, because at this stage the inner cell mass, which will develop into the fetus, has differentiated from the trophectoderm, which will later develop into the placenta and membranes. A biopsy at this stage involves the removal of a number of cells (3-10) from the trophectoderm. This type of biopsy is advantageous in that no cells are extracted from the inner cell mass, while still obtaining multiple cells for carrying out PGS, which leads to improved accuracy. Furthermore, blastocysts are more robust than earlier embryonic stages and tolerate biopsy exceptionally well. The blastocyst also is the best stage for vitrification (flash freezing, into a “glass-like” state) with a 95% survival rate.

What can we learn from PGS/PGD?

1. Obtain a 24-chromosome assessment in embryos with updated technology.
2. Detect chromosomal rearrangements such as reciprocal/Robertsonian translocations and pericentric and paracentric inversions which are well-recognized forms of genetic abnormality.
3. Detect known genetic disease with an identified mutation—PGD can be combined with your PGS cycle if needed. Preparation for this specific test is necessary prior to starting your IVF cycle (see above.)
4. Determine gender of embryos for family balancing purposes.

What is NOT tested with PGS or PGD?

• Birth defects (all newborns have approximately 3% risk for a congenital abnormality—“birth defect”—unrelated to known genes or disorders.)
• All genetic disorders. This technology does not allow us to screen for all genetic disorders. If you have a known specific genetic disorder, you must plan specifically for PGD, examining embryos to determine if they carry the same genetic disorder that you carry.
• Smaller chromosomal errors.

Why choose NRM for PGS/PGD?

• Minimize your chances of passing along a known genetic disease to your children.
• Potentially improve your chances of IVF success and minimize your chance of miscarriage.
• Improve your ability to select a single embryo to transfer, thus minimizing your risk of twins or higher-order multiple pregnancy.
• Your embryos will be biopsied by experienced embryologists, and testing will be performed using state of the art technology in order to get you accurate results in a timely and cost effective manner.

For more information on multiple pregnancy (twin, triplet and higher-order gestations), click here.

When you are ready, the next step is to schedule a consultation where we can meet with you and develop a personalized fertility plan designed to deliver the family of your dreams.

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