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Preimplantation genetic screening is a medical test on a fertilized embryo to check for signs of genetic disorders before performing an implantation. This allows the doctor to avoid implanting embryos with severe genetic disorders. This practice began developing as assisted reproductive technology and genetics improved, making it accessible to many couples seeking help with their pregnancies.
At the most basic, the goal of preimplantation genetic screening is to reduce risks for the couple. If a genetic disorder is likely to cause a miscarriage, the doctor does not want to implant the embryo, because it will expose the mother to the risks of pregnancy without the reward of a baby at the end. Severe genetic disorders incompatible with life are also a concern; a baby may only live for a few days or weeks after birth, and parents may not want to go through this.
The screening can also help parents avoid selective abortion, where they choose to abort after receiving a fetal diagnosis indicative of significant future health problems. Usually this occurs when a fetus shows signs of aneuploidy, an abnormal number of chromosomes. Depending on the chromosomes involved and whether the baby has too many or too few, this can result in severe genetic disorders. In other cases, the child may be born with disabilities that the parents do not feel equipped to manage.
In preimplantation genetic screening, doctors can check for aneuploidy, genetic conditions known to be a problem in a couple's family history, and specific genetic anomalies that a person may carry. The goal may be to prevent the implantation of an embryo that will have a genetic condition, or to avoid having a baby who will be a carrier. The screening can also be used to check for human leukocyte antigen (HLA) compatibility, to see if the baby can provide a donation of stem cells from cord blood for another sibling.
Preimplantation genetic screening involves some complicated bioethics issues. Bioethicists are generally in agreement about the safety of using testing to prevent high-risk pregnancies or situations where a doctor implants an embryo that is unlikely to mature. They are split on topics like using genetic screening for gender selection or to eliminate disabilities that are not incompatible with life. Parents, for example, could choose not to implant an embryo with genes associated with deafness. Some disability rights advocates express concerns that this technology could result in the elimination of some disabilities and a reduction in human diversity.
The bioethics issues lead most clinics to ask their patients to receive counseling before pursuing preimplantation genetic screening, to make sure they understand the procedure and have thought the ramifications through.