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Embryo Screening and In Vitro Fertilization
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In vitro fertilization developed over 30 years ago and is one of the most popular conceiving methods with couples having infertility issues. It’s conception under controlled laboratory conditions. Cells are placed in Petri dish, sperm fuse with egg and after conception is confirmed – fertilized egg is inserted into woman’s womb. Other method is intracytoplasmic sperm injection where sperm cell is injected directly into the egg. By now, around 5 millions babies are born after conceived using in vitro technique. Out if 100% babies born each year, 0.3% are test tube babies.

Pre-implantation genetic diagnostic or embryo screening is used to confirm the genetic “health” of the embryo. If genetic disorder is detected, egg will not be implanted and abortion will be avoided. This kind of tests could be performed on oocyte as well. When oocyte and sperm are used for screening, methods are known as oocyte and sperm selection. Pre-implantation screening can prevent: Duchenne muscular dystrophy, cystic fibrosis, fragile X syndrome, sickle cell disease, Charcot-Marie-Tooth disease, hemophilia A, Huntington's disease, just to name it few. When couple is at high risk of developing offspring with serious genetic disease(s), embryo screening combined with in vitro fertilization offer a solution by selecting healthy embryo that will be implanted afterwards.

There is couple of ethical issues associated with embryo screening and pre-selection. Human leukocyte antigen (HLA) matching is used to detect embryo that will match sick sibling and be able to donate umbilical cord blood stem cell for Fanconi anaemia, b-thalassemia or leukemia treatment. In other words, parents are making baby (by selecting right embryo) so they could use it for the treatment of their already born sick child. Sex related genetic disorders could be prevented (such as fragile X), but this kind of testing could be used by future parents also to decide which gender they prefer better. Some people having minor genetic disorder (like deafness) could select embryo that will develop same illness instead healthy one, because they want to share same characteristic with their offspring.

Pre-implantation tests are not 100% correct and accurate. When results of testing are done, overall conclusion is made by analyzing person’s medical history, family history and just finished genetic test. Mutations that are altering DNA are associated with numerous illnesses, but variations in DNA are happening naturally as well. Genetic polymorphism is not associated with any kind of disease but could make embryo screening inconclusive and difficult to interpret. Sometimes it’s hard to tell if genetic alteration is positive sign indicating future illness or simple polymorphism that wouldn’t affect health at all.

Usually, 2 days (6-8 cells stage) or 5 days old embryos (blastocyst stage) are inserted into the womb. Medium, where embryo is grown before implanting, contains glucose, vitamins, amino acid, cholesterol…all nutrients necessary for successful development. Depending on the woman’s age, health and the quality of the available embryos, usually 1 or 2 embryos are inserted. Some countries are approving implantation of up to 6 embryos which greatly increase the chance of pregnancy but also increase chances of multiple pregnancies.

Assisted zona hatching is used to help implantation process. Drilling the layer around egg will help egg hatch out once in uterus and ensure endometrial nesting. Hormone supplements (known as luteal support) are part of the treatment because progesterone, progestins and GnRH agonists can increase the chance of successful implantation and embryogenesis. After two weeks, if happened – pregnancy will be easily detected by blood or urine test. Today, 30% of in vitro fertilizations are finalized successful with healthy babies born at the end.

Cryopreservation is method used to preserve oocytes or embryos for the future in vitro fertilization cycles. Extracted oocytes or successfully fertilized eggs can be preserved by lowering the temperature below zero. Cryopreservation is useful when medical issues and treatments can decrease future success in pregnancy (chemotherapy is affecting ovaries and number of remaining oocytes). Couple that is going through in vitro fertilization can cryopreserve “leftover” embryos to be used in the next round in case first attempt doesn’t end up successfully. Cryopreservation is also used when eggs or embryos are planned for donation. Oldest successfully fertilized egg was stored for 16 years.

In vitro fertilization enables not just infertile couples, but single parents or gay couples to become parents. It is not cheap, simple and 100% successful method, but still raises the chance of pregnancy greatly comparing to other methods.
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