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. Vitrification very rapid freezing of embryos and eggs has been a huge benefit to us, but the technique is subtle and not everyone gets the same results. Clearly, monitoring of laboratory personnel is vital to a high quality embryology laboratory.
Quite honestly, the uterus is my best friend on a day-to-day basis. That is because it usually works. I say this because over the last 26 years, I have seen large numbers of sub-optimal appearing embryos make beautiful children.
They were suboptimal often because of patient parameters, but also because our treatments and our labs were less sophisticated, and the uterus rescued them.
The researchers likened this process to an "entrance exam" set by the womb — an embryo needs to pass this test in order to implant. But sometimes, the womb may make this exam too difficult or too easy, which could lead to the rejection of healthy embryos, or the implantation of embryos with development problems, the researchers said. The new findings may have implications for fertility treatment , because one of the main reasons fertility treatments like in vitro fertilization IVF fail is that embryos don't implant.
With future research into the factors that govern implantation, it may be possible to identify women at risk for miscarriage or other pregnancy complications by taking a sample of her uterus lining, said Jan Brosens, a professor at the University of Warwick in the United Kingdom. Human embryos are genetically diverse, and some have mutations that impair normal development. In some cases, these impaired embryos will not implant in the uterus, but often, they implant only to undergo miscarriage later.
The patient feels pressure, but typically there is no pain. For women who have undergone intrauterine inseminations IUIs , the sensation should be very similar. The transfer itself is a fairly simple procedure with very little discomfort. A thin, soft catheter is threaded through the cervix under ultrasound guidance, to be very exact in the embryo placement location, generally 1 to 2 cm from the top of the uterine cavity. After cleansing the cervix with solution, the doctor will place an empty transfer catheter through the cervix into position inside the uterine cavity.
Then the embryologist will bring the catheter containing the embryo s from the lab a few feet away, so we can minimize the time that the embryos are exposed. Once we have the embryo s , we feed the catheter with the embryo s through the empty catheter that is in place. On the ultrasound screen the patient will be able to watch the bubble of air and fluid the embryo is contained in get placed gently into the uterine cavity.
After placement of the embryo s , the embryologist checks the catheter under the microscope to make sure that the embryo s transferred properly. Then the patient can get up and go straight to the bathroom, if needed. After that, the embryos have to implant into the uterine lining on their own over the next few days, with the goal of developing into a successful pregnancy. Several recent studies have confirmed that immediate bed rest after the embryo transfer is completely unnecessary. Back in the s, after an embryo transfer, we prescribed that patients stay on complete bed rest for three hours and even rely on bedpans instead of going to the bathroom.
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