In-vitro fertilisation (IVF) and other fertility treatments help many couples and individuals achieve their goal of becoming parents. Embryology and IVF processes are highly specialised and rely on advanced science and technology – but they don’t need to feel confusing or inaccessible.

To make things clearer, we asked our expert embryologists, Mohsen Attia and Kyrillos Salib, to answer some of the questions we hear most often about what happens in our in-house laboratory. Kyrillos joined The Fertility & Gynaecology Academy in 2021. He plays a key role in our patient journeys, helping us deliver the highest standards of care.

How are embryos graded? Is grading the only factor when you select embryos for transfer?

Embryos are graded based on their appearance under the microscope. We look at factors such as cell number, symmetry, fragmentation on day three. For blastocysts (day five/six), we assess expansion, the quality of the inner cell mass and the trophectoderm. 

Grading helps us understand how well an embryo is developing, but it is not the only factor we use when selecting embryos for transfer. We also consider the patient’s medical history, previous IVF outcomes, the genetic status of the embryo (if testing has been done), and how consistently the embryo has developed over time. 

Good grading is reassuring, but embryos with slightly lower grades can still lead to healthy pregnancies. We have integrated AI embryo selection at The Fertility & Gynaecology Academy to empower our existing embryo assessment tools and improve outcomes.

What is PGT (genetic testing)?

Preimplantation Genetic Testing (PGT) is a technique used to analyse embryos for chromosomal or specific genetic conditions before transfer. 

A few cells are gently removed from the embryo at the blastocyst stage and either sent to a specialist genetics laboratory, or tested in-house.  The Fertility & Gynaecology Academy is one of the few fertility clinics in the UK which offers genetic testing in-house. PGT can identify chromosomal abnormalities, inherited conditions and the number of chromosomes present, helping reduce the risk of miscarriage and improving the chance of selecting an embryo with the best reproductive potential. It also helps prevent the transmission of genetic diseases from parents to their children.

Why don’t all embryos reach the blastocyst stage?

Embryo development is complex, and not every embryo will progress to the blastocyst stage. Several reasons explain why:

• Genetic and intrinsic factors: Some embryos stop growing because of chromosomal abnormalities such as aneuploidy. These issues occur naturally and can result from poor egg or sperm quality, slow or irregular embryo development, or damage to mitochondrial DNA. Many of these factors are inherent to the embryo and cannot be influenced externally.

• Extrinsic and environmental factors: Embryos are sensitive to their surroundings. Factors such as parental age can play a role, as chromosomal abnormalities become more common with advancing maternal or paternal age. In the laboratory, suboptimal conditions can affect embryo development. However, at The Fertility & Gynaecology Academy, we use time lapse imaging, meaning embryos remain in a stable environment throughout development, without being removed for assessment.

• Biological function: Embryo arrest can be viewed as a natural protective mechanism. If an embryo stops developing, it is often because it would not have resulted in a viable pregnancy. Nature uses this process as a form of quality control.

Does embryo transfer on day 3 or day 5 offer a better chance of success?

The best timing varies between patients and depends on factors such as embryo number, quality and medical history. Both approaches can lead to successful pregnancies.

Benefits of day 5 (blastocyst) transfer

• Blastocysts have shown they can grow to a more advanced stage, which may improve selection.
• Higher implantation rates are often seen because the embryo is transferred at a stage more closely matching natural conception.
• Blastocysts allow better synchronisation with the endometrium.

Benefits of day 3 transfer

• Ideal when embryo numbers are low, giving embryos the opportunity to continue developing inside the uterus.
• May help avoid the risk of all embryos arresting in the laboratory.
• Suitable for patients with previous poor blastocyst development.

Why didn’t all my mature eggs fertilise?

Not all mature eggs will fertilise, even when conditions are optimal. Fertilisation depends on several factors, including egg quality, sperm quality, timing, and the way the egg and sperm interact during ICSI or standard IVF. Some eggs may appear mature but still lack the internal structures needed for normal fertilisation. Likewise, sperm may be unable to complete the fertilisation process even if they look healthy under the microscope. This variation is entirely normal in IVF and something we see frequently. The Fertility & Gynaecology Academy has the ability to address this issue using calcium ionophore.