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Preimplantation Genetic Diagnosis (PGD)
Over the last 25 to 30 years, reproductive medicine has been revolutionized. Women are getting pregnant, and couples are having babies at a rate that we could not have even dreamt of years ago. Back in the 1970s and ‘80s we were doing surgery to try to fix infertility. Back in the last decade to two decades we have learned how to take eggs and sperm, put them together and grow them longer and longer until 96 hours in a dish they have become beautiful embryos and blastocysts that can actually be transferred and implant and become healthy babies.
Over the last few years the technology has improved even more. These days we’re not only looking at the structure and function of tubes and uterus, not only looking at the cells but we’re looking at the DNA itself. We’re testing embryos and we’re finding out which embryos are going to give us the healthiest babies, and which potentially can be disease carrying.
There are two different types of genetic analysis that we perform when we’re biopsying embryos and we’re learning about their DNA, one of which is to look for gene mutations. There are two types of genetic analysis that we normally do on embryos. One is looking for an abnormal gene that can cause disease, and one is to test whether the embryo itself is chromosomally normal or abnormal.
When we do preimplantation genetic diagnosis, when we biopsy an embryo and look for a certain disease, we’re looking for what’s called a single gene mutation. It could be cystic fibrosis, Tay Sachs, sickle cell disease. In general, when there is a abnormal gene in both the mom and the dad then the baby has a one in four risk of having that problem and expressing that disease, so what we’re able to do is biopsy an embryo while it’s in our dish, analyze the DNA and find an embryo that isn’t effected by that disease.
The other time that we’re actually analyzing embryos these days is to look to see which embryos are normal or abnormal. We know that especially with reproductive aging, the average 40-year old woman has the majority of her eggs having some chromosomal abnormality and these eggs can be fertilized and implanted and can lead to chromosomal problems or miscarriages or even babies born with Downs syndrome or other chromosomal variations.
We’re now able to analyze the embryo taking off a few cells from the outside of a 100-cell embryo and figure out which embryo is normal and which embryo is abnormal. This new technology, or preimplantation genetic diagnosis, is being done with a PCR-based technology called Comprehensive Chromosomal Screening. Now, no technology is going to be 100 percent accurate, but it has been incredible how well this technology has fared, really over the last year or so. We’ve been able to take a dish full of ten embryos and figure out the one that is destined to become a healthy child, and we’re able to not transfer ones that are destined to either miscarry or become a child that is affected by disease.
All of reproductive medicine starts with careful patient information, with analyzing all of the available information, and with a high tech laboratory that is capable of growing embryos, culturing them, tracking them, finding the embryo that is the most likely to end up in a healthy child and transferring that one to the patient.
This is a really exciting time in reproductive medicine. We’re able to prevent a lot of disease, we’re able to help couples have healthy babies, we are limiting miscarriages, and I think the future is even brighter.