Growing Embryos in the Laboratory
Egg Fertilisation & Culture
After the eggs have been collected from the ovaries, the eggs are stored in a warm incubator in the laboratory. Just a few hours later, the sperm will be introduced to the egg. The patient will recover at home whilst fertilization takes place overnight. There are two main ways to introduce the sperm to the egg. If there are male factor issues with poor quality sperm having been noted in the lead up to treatment, a specific technique called ICSI or intra cytoplasmic sperm injection may be required.
In the vast majority of patients, conventional insemination techniques can happen. This involves each egg being mixed with a fixed concentration of sperm in the hope that sperm will bind to the outside of the egg and naturally penetrate its outer shell leading onto normal fertilization. But in some circumstances, this would fail if undertaken with low quality sperm and therefore, ICSI has created a lifeline for many men with poor quality sperm to be able to create normally fertilised eggs.
We’ll look a little bit more at ICSI as we go through the course.
Once the eggs and the sperm have been introduced to each other, either through natural insemination or ICSI, they’ll then be cultured in a closed incubator overnight to see if they fertilise normally. Not every egg that is retrieved is mature, and not every mature egg will fertilise normally. ICSI doesn’t guarantee a hundred percent fertilisation and should only really be used when there are male factor issues, where sperm parameters are not optimum
The eggs that fertilise normally will be grown on in culture, in conditions that mimic that of the fallopian tube for between three to five days. A cleavage stage embryo at just two to three days old may be returned to the uterus by some clinics, but most of the very best clinics will be good at growing embryos right through to the blastocyst stage.
A blastocyst is more sturdy. It will also have the highest chance of success and ultimately, surplus embryos created from the cycle at blastocyst stage stand the best chance of being frozen and thawed for use in the future.
Screening Embryos (PGT-A)
Once the fertilised eggs reach the blastocyst stage, this is when the embryo transfer would normally take place. But some patients may choose to actually genetically screen their embryos for chromosomal abnormalities. This is not a technique that’s offered across the board with every patient, and it should be done just in patients who require it.
But let’s think about why it’s done. But far and away, the most common reason for an IVF cycle to fail or for implantation to not take place is due to the fact that the chromosomes within the embryo are not entirely normal. This will cause an embryo to either implant and fail to then continue to grow, or perhaps to continue to grow, but sadly result in a miscarriage. Pre-implantation genetic testing of embryos for what’s identified or termed as a normal or an abnormal embryo, is a common technique performed across many clinics. As patients get older, they’re much more likely to find that they release abnormal eggs, and therefore this will then feature in the embryos that they create in the laboratory. So some patients may opt at the Blastocyst stage not to transfer their embryos, but to genetically screen their embryos to try to identify the embryos which are chromosomally normal or euploid.
This, however, adds additional cost to cycles and does not in fact, increase the number of normal embryos that a patient has. But what it can do is reduce miscarriage, it can also reduce the time to reaching a live birth and a pregnancy. So it’s an additional add-on in treatment, which we will do in clinics, and you’ll need to ask your clinician very carefully if it’s appropriate for you when you are undertaking your treatment.