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What happens in the embryology lab?

When you’re going through fertility treatment, you are likely to be most familiar with your hormone injections, blood tests and scans.

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Written by Apricity Team

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    When you’re going through fertility treatment, you are likely to be most familiar with your hormone injections, blood tests and scans. Regardless of which fertility treatment pathway you’re on, intrauterine insemination (IUI), in vitro fertilisation (IVF), intracytoplasmic sperm injection (ICSI), egg donation or surrogacy, you may be wondering what happens to your eggs, sperm and embryos in the lab. In this article, we will walk you through each procedure that happens in the embryology lab step by step. 

    These include:

    1. Egg collection

    2. Sperm preparation

    3. Fertilisation: in vitro fertilisation (IVF) or intracytoplasmic sperm injection (ICSI)

    4. Embryo monitoring

    5. Embryo transfer

    6. Embryo, egg and sperm cryopreservation

    Step 1. Egg collection

    Once your ovarian stimulation period is over and your doctor and nurses have confirmed that they are able to collect a desirable amount of eggs (between 6 and 15 eggs is considered to be the average number 1) you will have your egg collection. It is a procedure where a special needle is passed through the wall of the vagina into the ovary and, with the guidance of ultrasound, the fluid of each follicle(a small sac in the ovary containing an egg)  will be collected. The follicular fluid is passed on one by one to an embryologist in the lab so they can search for the eggs. 2

    Prior to egg collection, both the person performing egg collection and the embryology team know approximately how many eggs to expect based on the most recent ultrasound scan. So when all follicles have been drained of fluid, the embryologist confirms how many eggs have been collected and lets you know straight away after the procedure is finished. 

    The egg collection procedure lasts around 20 minutes and you will be given sedation medicine to  minimize any discomfort. 

    Step 2. Sperm preparation

    While the female patient is in the egg collection room, the male partner is asked to produce a fresh sperm sample in a private room. An andrologist in the lab will examine and wash the sperm so that the healthiest and most active sperm are selected for fertilization. If you are having treatment with frozen or donor sperm, it will be carefully thawed in preparation for fertilisation. 

    Find out more about male diagnostics

    Step 3. Fertilisation: IVF or ICSI

    The next step after the eggs have been collected and sperm has been prepared is fertilisation. In the embryology lab, fertilisation is done either by IVF or ICSI on the same day after the egg collection. 

    In the case of IVF, the collected eggs are mixed with the partner’s or donor’s sperm in a sterile dish containing special fluid called culture media. The sperm will swim towards the egg and merge with it thus achieving fertilisation. 

    If the sperm quality is low, intracytoplasmic sperm injection (ICSI) will be recommended. In this case, a single sperm is selected in turn and carefully injected directly into an egg, thus significantly increasing chances of successful fertilisation. This process is repeated for each available collected egg. 

    The next day, the embryologist will confirm whether the eggs have been fertilised and if so how many embryos were created. 

    Step 4. Embryo monitoring

    During the next 5 days, the embryos are closely monitored in incubators. Some labs may have time-lapse monitoring incubators that allow the embryologists to observe the whole embryo development virtually through a series of captured images.. 

    The embryos are kept in special embryo culture media. The media is made out of many proteins, compounds that provide energy (e.g. glucose), antibiotics and many other supplements that nurture the embryo. The aim of a good culture media is to mimic the natural embryo environment of the female reproductive tract as closely as possible. 

    Throughout the next 5 days, the embryos divide from one cell to four cells, then eight cells and so on, until it starts to form a blastocyst (which usually occurs by day 5). A blastocyst is unique because it already has two distinct, essential structures:

    • Inner cell mass which will become the the foetus

    • Trophectoderm which will become the placenta

    Which day and stage your embryo will be selected for transfer will depend on your clinic’s protocols, but embryo transfer is usually performed on day 5, at the blastocyst stage, where the chances of  implantation are the highest.

    Step 5. Embryo transfer

    The best-quality embryo will be selected for embryo transfer. One embryo is generally transferred in order to minimise the chance of multiple pregnancy and its associated risks, although two embryos can be transferred in women with previous failed transfers or over 37 years of age.

    Using a thin tube called a catheter, the embryo will be passed through the vagina and the cervix and placed into the womb.

    Embryo transfer is a much simpler procedure compared to egg collection and usually resembles a cervical smear test, so you will not be sedated. 

    Step 6. Cryopreservation

    If any healthy embryos are not transferred, either due to patient wishes or for medical reasons, they will most likely be frozen and stored for future frozen embryo transfers. 

    You can also freeze your sperm or eggs before fertilisation and store them for future use.

    The embryos, eggs and sperm are stored in liquid nitrogen at very low temperatures, usually around 196°C. This allows them to remain unchanged and healthy until they are thawed for a frozen embryo transfer (FET). 


    Each member of the embryology team works really hard to ensure your eggs and sperm, and the resulting embryos are safe and well taken care of, and will result in positive pregnancy rates. Thanks to scientific and technological advances, lab practices are constantly improving and making it possible for more people to have children. 

    At Apricity, we are proud to be working with a trusted network of top embryology lab teams in HFEA-licensed clinics based in London and Manchester. Our partner clinics are focused on giving every patient the best possible outcome through carefully tailored treatment plans. 

    Written by Apricity Team

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