Preimplantation Genetic Screening for Chromosomal Abnormalities
Dr. Mark Johnson explains that the majority of human conceptions are lost in early life because of chromosomal problems with the embryo. At Arizona Associates for Reproductive Health, we provide preimplantation genetic screening to test for aneuploidy and other chromosomal abnormalities. These early-stage screening tests allow us to better understand causes of infertility.View transcript
The majority of human conceptions are actually lost in early life because of chromosomal problems associated with the embryo. Now it's not necessarily the embryo's fault that it received abnormal genetic information, either from the egg or from the sperm. But the embryo is what we try to evaluate when we do chromosomal pre-implantation genetic screening, looking for what we call aneuploidy or abnormal chromosome complement in the embryos. So the majority of human embryos that are lost are related to the chromosome problems that cause them their early demise. In some cases, these can be embryos that are lost in the first two weeks after ovulation. So you'll never even know that you conceived during that cycle. All you have is onset of your menses or a negative pregnancy test. Other abnormal conceptions end up as miscarriages or lost before the first three months of life. So it's important for us to be able to screen embryos for chromosome abnormalities, and that's where the Holy Grail of chromosomal screening comes into play that's been developed over the past few decades. Today, we biopsy embryos at the blastocyst stage, allowing us to remove four to six cells, maybe even a few more cells to allow for the DNA analysis of the embryo. In general, the embryo is frozen immediately after the biopsy, but in some cases it can be transferred within 24 hours if the analysis results are known. In most cases, it takes a little bit longer for the DNA analysis to give us results about the embryo. At any rate, the nice thing about this type of screening is it can filter out those abnormal embryos and those abnormal conceptions that occur prior to us transferring them back into the uterus and producing a pregnancy. When we transfer back a single embryo into the uterus that's now been shown to be chromosomally normal, not only are we confident with a high degree of confidence that it's going to implant and produce a baby up to a percentage of around 65/70 percent per transfer. Another reason couples may want to consider pre-implantation genetic screening of their embryos for the chromosomal complement is the increasing age of the woman. As the woman goes through the normal aging process, there is a higher risk that the eggs that she produces are chromosomally abnormal and thus carried over into the embryo causing the embryo to be abnormal and suffer its fate from those abnormalities.