Throughout the course of your treatment here there will be a lot of medical terms and acronyms thrown at you. You will have probably heard a few of them before, but just in case I wanted to explain some of the terms we will be using. If you are feeling a little like you are drowning in a medical soup, don’t worry, you should be up and treading water by the time I am done with you. I will be highlighting some of the more important terms and describing where in the process they will be coming up.
First of all there is the biggie – “IVF” or the test tube baby process itself, which I am sure most people have heard of by now. It stands for In Vitro Fertilization – the in vitro part being Latin for ‘in glass’. Now there are not many people that even use glass dishes anymore, but in vitro has become a phrase for any medical or scientific procedure that occurs outside of the body and in the laboratory. The test tube baby phrase itself is also a little of a misnomer as most people probably use dishes rather than tubes these days as well.
IVF not only stands in as a blanket term that covers everything, from blood draws to laboratory work, that are carried out over the course of a few weeks to get you pregnant but also to signify one way in which the eggs can be fertilized after the retrieval. What we mean when we say ‘IVF fertilization’ is that the sperm will be prepared to a specific concentration and then just added to the dish with the eggs and allowed to get on with its job of swimming to the egg and fertilizing it. This is opposed to ‘ICSI’, which stands for Intra Cytoplasmic Sperm Injection which is utilized when there are either a low number of sperm, they are not swimming very well or there have been previous fertilization issues seen. With ICSI we actually isolate and pick up a single sperm which we inject right into the egg to allow for fertilization to take place. Allowing many more couples the chance to conceive their own biological offspring than would be possible with just IVF fertilization alone. Pretty nifty, if you ask us!
Moving on to the egg retrieval day, we take oocytes (eggs) and then add the sperm to fertilize them. We check to see whether they have fertilized the morning after the egg retrieval, which the laboratory refers to as day 1. At this point in time we are looking for the evidence of pronuclei. The pronuclei (or PN) are the nucleuses, the structures that hold the genetic information of both the sperm and the egg, and they signify that fertilization has taken place – they can be seen about 18 hours after insemination. Sperm and eggs are haploid – they only have half of the genetic compliment of chromosomes that are needed to make an embryo so after the appearance of the pronuclei then they will fuse and the embryo (fertilized egg/oocyte) is on its way!
The egg is made up of a few different components, the most important of which you need to know about are the zona and the cytoplasm. The zona is most easily referred to as the shell of the egg – it is the outermost level that keeps the embryo intact until it completes division and hatches or breaks free ready for implantation. The other part is the cytoplasm which is a gel like substance surrounded by a membrane that comprises all the necessary components of the cell including the nucleus.
The next stage for the little embryo(s) is to cleave or divide which happens numerous times over the next few days while they are here in the laboratory with us. The first division is when the contents of embryo split into 2 parts – the chromosomes (cell blueprint) are duplicated and then they are split so that each of the 2 halves has the same number of chromosomes. This division continues as each cell duplicates and then divides. In this way the number of cells continues to double, ending up with 2-4 cells on day 2 and then 6-8 cells on day 3.
Next up, we will bring you into the clinic on day 3 to talk with you about your embryos and try to help you decide how many and when you should transfer. Your embryos will have been graded at this point and so will have been allocated a score based on the way that they have divided. We will have assessed the percentage of fragments in them as well – the less fragmentation the better. I liken fragments to breaking a bread roll and getting crumbs, as in when the cytoplasm divides there can be small parts of it that falls apart. Some fragmentation is OK, so don’t worry if your embryos have this happening.
The next major developmental stage for the embryos is the blastocyst which occurs by day 5 and is the last stage of development that we culture to before either transferring back into the uterus, or freezing for a future FET (frozen embryo transfer). In general a human blastocyst contains about 70-100 cells, and at this stage they have differentiated into 2 distinctly different cell types. There is the inner cell mass which is a tight bunch of cells that actually becomes the embryo. Meaning it becomes all the structures of the actual baby. The other area is the trophectoderm, which is a single layer of cells making up the spherical shape that works to implant the embryo onto the uterus and is integral in forming the placenta.
I hope this was helpful to explain some of the terms we use around here. If you have a term that you are confused about you can check out our glossary or ask in the comments below.