What Is ICSI – Intra-Cytoplasmic Sperm Injection?
An egg is a single cell. It has a shell around it (the Zona Pellucida) and inside the shell is a membrane that holds the cytoplasm. The Cytoplasm is the stuff that holds all the important bits of the egg, the nucleus (where the DNA is), mitochondria (the powerhouse of the cell, to give it energy) and all the other bits and pieces.
When the egg is ovulated (released from the ovary), it is picked up by the fimbria (little hand like bits at the end of the fallopian tubes), and it makes its way down the fallopian tubes.
It has a cloud of cells surrounding it called the cumulus cells, and closer to the zona are another group of cells called corona cells.
In natural fertilisation, the sperm make their way through the cumulus cells, then through the corona cells and finally meet the zona and one sperm makes its way into the cytoplasm. This process is a little bit like an interview process for the sperm, and only one ever actually makes it all the way through to the cytoplasm.
Image: Lennart Nilsson
How is ICSI different from IVF?
The eggs are retrieved directly from the ovaries in IVF, but they are still surrounded by this layer of cumulus and corona cells. Suppose your clinic is doing ‘standard IVF’. In that case, the eggs will be left with these cells on, and they will be placed into a culture dish, in some special culture media (fluid), which is designed specifically for fertilisation. The sperm will be allowed to ‘do their thing’ overnight… making their way through the layers of cells and finally allowing ONE sperm to enter and hopefully fertilise each egg.
In ICSI, we need to remove these outside cells (the cumulus and the corona cells) so that we can have a good look at the egg and see which ones are ready to be fertilised. The removal of these cells is done with a substance called hyaluronidase and special glass pipettes that helps to strip the cells off the outside of the eggs gently.
Eggs can be at varying stages of maturity:
GV (Germinal Vesicle): immature and not ready to be fertilised
MI – Paused at metaphase one: not ready to be fertilised
MII – at Metaphase 2 and ready to be fertilised
Degenerate – an egg is dead or dying and not able to be fertilised
ICSI injection needs to be done within a certain time of the trigger injection (the last injection you have before your egg collection) – usually within 42 hours of your trigger, so it’s all very time-critical.
The GV eggs will not mature any further outside of the body in time to be fertilised.
MI eggs have the possibility of maturing in the few hours between egg retrieval and ICSI, but success from these eggs is quite limited.
MII eggs are the ones that are injected, and we hope to get at least 80% of these fertilised.
The process of Intra-Cytoplasmic Sperm Injection is a very specialised one that takes many months to learn.
The eggs and sperm are loaded into a dish in separate droplets of culture media, covered by oil.
How does the Intra-Cytoplasmic Sperm Injection process work
The microscope that is used takes up a whole table a little bit smaller than a 6 seat kitchen table, and an embryologist does the procedure with years of training. The microscope sits on special feet to reduce any vibrations, and the table has special legs to reduce any vibration further. All of the manipulations are done with hydraulic control. So a normal movement with your hands translates to a tiny, tiny movement in the dish where the eggs and sperm are.
The embryologist first ‘catches’ a sperm and sucks it up into a tiny, tiny pipette, then very gently and carefully ‘holds’ the egg (again using suction) and injects the sperm into the egg, releases the egg from the suction and moves it to another spot in the dish (so that it doesn’t get a second injection!)
If there are plenty of sperm, then this process doesn’t take too much time at all. Usually a couple of minutes per egg, but if there is not much sperm at all, the embryologist might choose first to find all of the sperm needed and place them together in a dish before loading the eggs onto the dish and injecting them.
I remember a case once where 3 embryologists were searching for 2 hours to find sperm… we eventually found 3 sperm and injected the 3 eggs…. it was a very long afternoon!
It takes about 6 months to learn how to do ICSI and then a further year of supervised injections before you are allowed to do it on your own. In the UK, embryologists are required to get an ICSI licence from the governing body, the HFEA (Human Fertilisation and Embryology Authority).
Your embryologists are amazing!
Written by Lucy Lines at Two Lines Fertility