There are many potential causes of errors. If implantation does not occur, the endometrium breaks down and sheds, along with the blastocyst , as part of the menstrual cycle. However, if a blastocyst does implant, then the endometrium remains in the uterus , and together with uterine tissue, becomes the maternal portion of the placenta , called the deciduas.
Once the blastocyst adheres to the uterine wall, the trophoblast secretes enzymes that digest the extracellular matrix of endometrial tissue. The trophoblast cells then begin to intrude between the endometrial cells, attaching the blastocyst to the uterine surface. Further secretions of enzymes allow the blastocyst to bury itself deeply among the uterine stromal cells that form the structural components of the uterus. Subsequently, trophoblast cells continue to divide and form two extraembryonic membranes.
These membranes form the fetal portion of the placenta called the chorion. Additional enzymes and signaling factors secreted by these membranes remodel the uterine vasculature to bathe the fetal or embryonic blood vessels in maternal blood.
Chorionic villi are the folds of tissue and blood vessels that connect maternal and fetal blood pools. Maternal blood diffuses into the villi, and it travels through them into the fetus 's vasculature. Similarly, fetal blood diffuses from the villi and into the maternal vasculature. Normally fetal and maternal blood do not mix, but the relationship between the two circulatory systems enables the transfer of nutrients and oxygen to the fetus or embryo, and carbon dioxide and urea from the fetus to the mother.
While unique to mammals as a reproductive process, implantation is not unique to the uterus and the trophoblast. In the s, researchers found similarities between the invasive abilities of blastocysts and those of cancer cells.
The same trophoblast enzymes that digest the endometrium are also used by tumor cells to burrow into tissues throughout body. Tumor cells use the same growth factors as the trophoblast to attract maternal blood vessels, which then interact with the chorion , and to provide nutrients to the expanding mass.
In addition, the changes in the endometrium during decidualization such as swelling, the accumulation of white blood cells, and the general activation of the maternal immune system, are consistent with a response to the presence of pathogens or tumors.
Keywords: Reproduction , Human development , Fertilization. The Process of Implantation of Embryos in Primates Implantation is a process in which a developing embryo, moving as a blastocyst through a uterus , makes contact with the uterine wall and remains attached to it until birth. Sources Bischof, Paul, and Aldo Campana. Over the last two decades, various approaches to try and address this problem have been developed. All of these approaches have utilized in vitro fertilization with the embryos being tested.
For many patients, the testing allows us to accurately address the problem of embryos having abnormal chromosome numbers. How can this be? Today, we are going to explore why chromosomally normal embryos may not implant and how we try to address the problems when we can. Failure to achieve a successful pregnancy with euploid embryos can be generally grouped into three major areas: embryonic, uterine, and systemic.
The development of an early embryo is a complex and highly synchronized series of events to prepare it for attaching to and invading the lining of the uterus. The process starts at fertilization with single cell called a zygote, which develops over 5 days into a cell hollow ball, called a blastocyst.
It is a blastocyst that will attach to and implant in the lining of the uterus. Our 46 chromosomes contain about 25, genes that have to function properly to have the embryo develop successfully. I think of it like a symphony of the genes being turned on and off at specific times. If the timing of this is off, just like an orchestra, things will go badly. Basic science studies suggest that energy function metabolism of the embryo is also a likely cause of failure, but this too cannot be practically measured in the clinical lab.
Basic science studies and our clinical experience suggest that early embryo development can be altered by our clinical and laboratory environment. It is clear that the type of follicular stimulation in an IVF cycle will impact the oocyte and embryo.
The correct use of supporting medications LH or low dose-hCG, growth hormone, androgens may be beneficial to development of the growing follicle and egg for some individuals. However, incorrect use of these medications can be detrimental. The type of trigger shot used to prepare for egg retrieval hCG or GnRH agonist may have an impact on egg quality also, but who may benefit from which drug and to what degree there is an advantage remain unclear.
As you can imagine, the laboratory environment plays a huge role in how the embryos will perform. Culture media has evolved tremendously over the last 30 years, starting from simple media adequate for most cells to the variety of high quality embryo-specific, commercially made media that we currently use. There are several high quality culture media available that work well however, constant quality testing is essential to make sure a chosen media performs optimally.
The incubators that the embryos grow in and their function are clearly a major factor. Most high quality practices are using the small bench top incubators which do a better job of maintaining the chemical environment and temperature stability for the embryos to grow in. However, these high-tech devices must be constantly monitored, as subtle changes can impact embryo performance. Simple things like how often the embryos are evaluated, under what conditions, and the time it takes to do so can tremendously impact embryo performance.
The trend is clearly towards evaluating the embryos less frequently. It should not go without saying that technical competence of the people in the laboratory is essential for good outcomes.
However, those of us who have done inspections have seen a wide array of skill levels. In ICSI intracytoplasmic sperm injection- injecting the sperm in to the egg for example: was the procedure done at the correct time? What kind of sperm was selected? Was the sperm inserted in the correct place in the egg?
How long was the oocyte egg out of the incubator? Embryo biopsy for testing the chromosomes is a very demanding technique that requires a great deal of practice and experience. Chances are the failure is not due to anything you could control. Your fertility specialist will explain what may have happened and what you can do next. Here are some common reasons why an IVF cycle fails. The major reason why an IVF cycle is not successful is embryo quality. Many embryos are not able to implant after transfer to the uterus because they are flawed in some way.
Even embryos that look good in the lab may have defects that cause them to die instead of growing. This affects her chances of success with IVF as well. On average, only about 25 percent of transferred embryos go on to result in live births of babies. Women under 35 using their own eggs for IVF have an implantation rate of about 45 percent. Women 40 to 42 years old using their own eggs have only about a 15 percent chance of implantation.
Older women who use donor eggs, which are donated by younger women, have success rates with IVF that are nearly the same as those of younger women. Egg quality is all-important to having healthy embryos, and younger eggs usually have better quality. Especially if a woman is over 37 or has higher FSH levels she may not produce enough eggs to result in a number of embryos for screening and potential implantation.
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