It is normal that not every egg retrieved at egg collection will be mature, or be able to fertilise normally. After the eggs have been inseminated with sperm via In Vitro Fertilisation (IVF), or Intracytoplasmic Sperm Injection (ICSI), they are left uninterrupted and assessed the next day for signs of fertilisation. The embryologist will observe each egg and look to identify the presence of pronuclei (PN). Pronuclei represent the presence of the genetic material (DNA) within the fertilised egg (zygote). A successfully fertilised egg will have two pronuclei (2PN), one from the egg, and one from the sperm. Some eggs may present with an abnormal number of pronuclei, containing too little (1PN), or too much (3PN+) DNA. Embryos resulting from abnormally fertilised eggs may have reduced pregnancy potential, or an increased risk of leading to miscarriage. All normally fertilised eggs (2PN) will be kept and grown in the lab, while abnormally fertilised eggs will be discarded or monitored in the lab depending on the type of abnormality present. The 2PN stage is an important milestone in embryonic development, as it signifies successful fertilisation and the potential for further embryonic development.
When performing intracytoplasmic sperm injection (ICSI), the embryologist seeks to select the best quality sperm for injection into each mature egg. Selecting the best quality sperm increases the chances of successful fertilisation and embryo development, leading to a higher likelihood of a successful pregnancy. First, the sperm is prepared in the lab by removing the seminal fluid and other debris to concentrate the sperm. The sperm is then observed under high powered magnification to assess the morphology (shape, size and structure) and the motility (ability to swim). At Oasis, your specialist may also recommend the addition of Sperm Slow solution to assist in selecting sperm with good DNA maturity. High levels of DNA fragmentation have been associated with reduced fertility and poor pregnancy outcomes.
Embryo grading is an important part of the In Vitro Fertilization (IVF) process. It involves an embryologist assessing the appearance of a patient's available embryos to determine whether they have reached key developmental milestones and are suitable for transfer into the uterus or freezing. This process helps identify embryos with the greatest potential to result in a pregnancy, supporting embryo selection and reducing time to pregnancy. In addition to assessing embryo morphology, we also evaluate time-lapse imagery to gain a more comprehensive understanding of embryo development over time, rather than relying on a single static image.
At Oasis Fertility Centre, embryos are graded on Days 3, 5 and 6 after egg collection and insemination.
Day 3: On Day 3, ideally embryos should have developed to contain between 6 to 12 cells. The embryo is assigned a grade reflecting the quality of the embryo. Grade 1: < 10% fragmentation, even cell size Grade 2: 10-25% fragmentation, some uneven cell sizes Grade 3: > 25% fragmentation, uneven cell size
Days 5 & 6: On days 5 & 6, the embryos should have developed to the blastocyst stage. Blastocysts are composed of hundreds of cells which are separated into two different structures. Some cells form the inner cell mass (the structure that becomes a fetus), and the other cells form the trophectoderm (the structure that forms the placenta). At the centre of the ball of cells is a fluid-filled cavity. At Oasis Fertility Centre, the internationally-recognised Gardner grading system is used to grade embryos at the blastocyst stage. This grading system involves assigning a code to each blastocyst, acting as a description of their developmental stage and the quality of the inner cell mass and trophectoderm cells. Developmental stage: 3: Early blastocyst. The fluid-filled cavity at the centre of the embryo is small. 4: Expanded blastocyst. The cavity has gained more fluid and has expanded. This causes the cells of the embryo to press closely against its shell, resulting in the shell thinning. 5: Hatching blastocyst. The cavity has gained more fluid. The increase in pressure results in rupture of the shell and the embryonic cells begin to hatch. 6: Fully hatched blastocyst. The embryo has completely hatched out of its shell.
Inner Cell Mass Grade: A: The inner cell mass is large and composed of many, tightly packed cells. B: The inner cell mass is moderate in size and composed of several cells. The cells may be loosely compacted. C: The inner cell mass is small and composed of very few cells with little to no compaction. Sometimes, the inner cell mass is absent.
If your embryo develops into a high-quality blastocyst on day 6, we will not perform a fresh embryo transfer in the same cycle. Instead, we will freeze the blastocyst for future use in a frozen embryo transfer (FET) to correct for its' delayed development and ensure the embryo is reaching the uterus when it is most receptive to implantation. This gives the embryo the best chance for success.
No, we do not perform rescue ICSI at Oasis. As we cannot confirm if a sperm has already entered the egg via IVF, adding another sperm at this point could result in an abnormal embryo.
Not all eggs collected during IVF are guaranteed to be mature. While follicle size and hormone tracking are used to determine the optimal time for egg collection, not all eggs will develop at the same pace. Although medication and the trigger injection are carefully timed to help the eggs mature, even larger follicles may not always contain a mature egg. Cycle outcomes can be discussed with your treating specialist in a review appointment to assess indiviudal circumstances.
No, we cannot inject immature eggs as they do not have the potential to fertilise normally. A mature egg has undergone a maturation process where it removes half of its genetic material to make space for the DNA from the sperm. If an egg has not undergone this process, it will have too many chromosomes and will not result in a viable pregnancy.
It is difficult to determine why an embryo did not survive. When grading embryos for freezing, we assess them based on their development stage and the quality of the cells visible at the time of freezing. Although a good quality embryo should typically survive the freeze, this outcome could indicate that the embryo had abnormalities. However, each embryo can respond differently to the freezing/thawing process, so it does not necessarily mean that your other embryos will have the same outcome.
Day 3 and Day 5 embryos refer to the age of the embryo in vitro, meaning the number of days since fertilisation of the egg in a laboratory setting. A Day 3 embryo, also referred to as a cleavage stage embryo, is typically a 6-12 cell structure. By Day 5, an embryo will hopefully have undergone many cell divisions, having hundreds of cells, and now be referred to as a blastocyst. Blastocysts have an identifying fluid-filled cavity surrounded by a layer of cells. At this stage, the inner cell mass has formed and will eventually develop into the embryo, while the outer layer of cells will eventually form the placenta. Not every embryo will reach the blastocyst stage, this is a normal and expected outcome of extended embryo culture. Some embryos will arrest in development which will help deselect against the poorer quality embryos lacking the potential for pregnancy. In summary, the main difference between a Day 3 and Day 5 embryo is the degree of development and differentiation of the cells.
In order to be suitable to freeze, an embryo must meet standardised criteria which has been set to ensure only embryos with the potential for pregnancy are stored for future use.
Embryos need to have reached set developmental milestones, as well have a suitable embryo grade. Poor quality embryos, such as those that have poor cell division, do not have the potential to lead to a viable pregnancy. They are also less likely to survive the freezing and thawing process and are therefore not suitable for storage. It is important to note that not all embryos are suitable for freezing and that the quality of the embryo at freezing may affect how well the embryo survives the thawing process. Typically, it is expected that 90-95% of frozen blastocysts will survive the process.
IVF (in vitro fertilisation) and ICSI (intracytoplasmic sperm injection) are two methods used to inseminate eggs in the lab. In standard IVF, eggs are placed together with many sperm overnight and fertilisation occurs without direct intervention. In ICSI, a single sperm is selected and carefully injected directly into each mature egg to help achieve fertilisation. ICSI is often recommended when there are sperm-related issues or when poor outcomes were seen in previous IVF cycle/s. Aside from the method of insemination, care of the embryos and the rest of the treatment cycle proceed in the same way for both IVF and ICSI.
MIRI is a specialised time-lapse incubator used for all Oasis patients. It continuously monitors embryos as they develop, without disturbing their delicate environment. This allows our Embryologists to observe each embryo’s development and cell division patterns, helping guide decisions about which embryos are prioritised for transfer or freezing.
Yes, Oasis currently offers PGT-M, PGT-SR and PGT-A for eligible patients.
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