More and more reproductive institutions are using Preimplantation Genetic Diagnosis (PGD) to greatly increase the chances of successful pregnancy for couples who have previously failed in vitro fertilization. It is estimated that more than half of failed IVF cases cannot be explained by obvious issues with embryo quality. However, this statistic can be misleading for many couples. Most IVF centers carefully observe the appearance of embryos under a microscope, as they try to identify the "good" or "high quality" embryos from the poorer quality ones. Typically, "good" embryos are labeled once they show the appropriate amount of cell division at a given point in their growth cycle.
Preimplantation genetic testing provides doctors with an unprecedented ability to examine embryos beyond their surface appearance. We can now inspect the most important internal genetic code of the embryos. With these new genetic tools, we have learned that certain embryos which appear to be of the highest quality on the surface may carry genetic codes that make them less than optimal for establishing a healthy pregnancy.
Preimplantation genetic testing improves success rates in a single IVF cycle
By transferring two or three embryos that are known to have normal chromosomes, the chances of successful pregnancy in a single IVF cycle can increase significantly. When using embryos that are known to be genetically normal, the chances of a healthy pregnancy can double.
Preimplantation genetic testing can greatly improve implantation rates (the chance of a single embryo resulting in pregnancy). Embryologists use preimplantation genetic testing analysis to determine whether the embryos have normal chromosomes before selecting which one to transfer to the mother. In embryos that are normal in their genetics, each of the 22 types of chromosomes should have two (and only two) chromosomes, with one set of XX female chromosomes or one set of XY male chromosomes. Any more or less than this will lead to a faulty embryo.
Preimplantation genetic testing allows us to take an important step forward by identifying and isolating embryos that are chromosomally normal. With these critically important genetic pieces of information, we are in a good position to determine which embryos offer the best chances of a healthy pregnancy. By analyzing embryos with preimplantation genetic testing, we can offer significant improvements to IVF success rates for those who've had prior attempts.
Accuracy of preimplantation genetic testing in failed IVF cases
Preimplantation genetic testing has over 98% accuracy in detecting genetic abnormalities. Since Preimplantation genetic testing can improve success rates for IVF, many couples choose to reduce the total number of embryos placed in the uterus, which also reduces the chance of multiple births and premature delivery. Experience has shown that even with fewer embryos implanted, the pregnancy success rate is still increased after Preimplantation genetic testing.
Preimplantation genetic testing identifies sperm or "both-sided" infertility issues
Another very important issue learned from preimplantation genetic testing is that although sperm is rarely associated with IVF failure, in some cases it may cause repeated IVF failure. While many sperm deficiencies prevent fertilization of the embryo or halt development before the blastocyst stage, more subtle microdeletions and sperm chromatin fragmentation may explain why some IVF cycles fail despite having several preimplantation genetic testing normal embryos to choose from. With this new information, sperm chromatin fragment and microdeletion screening can be considered in certain IVF cycles to eliminate potential undetectable sperm defects.
Sometimes, when it is discovered that a single sperm or sperm and egg together are causing infertility or repeated IVF failure, the notion of which partner is "at fault" will be upturned. Pre-implantation genetic testing and its wide application will deepen our understanding of human embryo development and provide more opportunities to help more couples.
Preimplantation genetic testing provides a true scientific basis for selecting embryos for IVF and understanding how and why some couples experience repeated failures. When no chromosomally normal embryos are selected, the chances of success are slim and energy can be diverted into seeking other means of achieving pregnancy.
Overall, any program that improves success rates will save time and money in the long run, and reduce the emotional cost of dealing with infertility. Non-integer screening with preimplantation genetic testing is neither simple nor cheap, but for many couples the benefits clearly outweigh the costs.
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