STP Specialisms – Embryology

What is Embryology as a clinical field?

Fertility treatment has been an established medical specialism for over four decades, yet many people are unaware of what it entails, and the role clinical and non-clinical staff play. An IVF clinic combines the skill sets of consultants, specialist nurses, and scientists to assist couples trying to conceive. The latter is where I come in. Hi! My name is Laurie-Anne, and I am a second-year Embryology trainee (Reproductive Science) at University Hospitals Coventry and Warwickshire NHS Trust. I’m going to show you what a day in the life of an Embryologist is like and how we contribute to fertility treatment.

A common misconception I encounter when people ask me about my job is that an Embryologist does everything; from collecting the eggs from the patient to ultrasound scanning and taking blood work. I wasn’t aware that ‘embryology’ was a specific job role before applying for the STP and presumed the laboratory work was completed by specialised clinicians. Embryology is more patient-facing in comparison to other specialisms, but our main role as embryologists is in the laboratory with the gametes (sperm and eggs) and the embryos. We talk to patients before their theatre treatment and on the phone to provide treatment updates, but we mainly work with our Petri dishes. Embryologists are involved in the entire patient pathway from treatment planning to embryo transfer and embryo freezing. As a multidisciplinary team, we work together to ensure each patient has a successful treatment cycle.

Daily tasks – keeping the lab running smoothly…

Like all laboratories, we want to maintain a clean environment for cell cultures. All laboratory staff wear scrubs, scrub hats, and change our shoes when we enter the lab. This is increasingly important when creating and culturing embryos. Eggs, sperm, and embryos are fragile when removed from their normal in vivo environment, so a lot of care is taken to replicate the in vivo female reproductive tract conditions in the laboratory.

The daily look: scrubs, scrub cap, and mask (Covid edition, minus the visor)

Every workstation is temperature-controlled, and the incubators have a specific concentration of oxygen and carbon dioxide they are maintained at. The laboratory equipment is rigorously monitored by external systems and sterilised frequently. Even the air in the laboratory is monitored daily to reduce harmful chemicals and microbes. Sterility and gametes/embryo viability is something we are constantly considering.

One of the first things we learn is laboratory set-up for treatment cycles. We prepare culture dishes for each patient, utilising culture media designed for each stage of embryo development. These are prepped the day before use to ensure they are warm and equilibrated for the eggs, sperm, and embryos.

Turning gametes into embryos

Our first contact with the patient is at the egg collection. Specialist consultants use ultrasound guidance to aspirate fluid from the ovarian follicles. This fluid is passed to us in the laboratory in tubes. Using microscopes within the workstation, we search the follicular fluid for the eggs, shouting through to the theatre when we find them. We keep track of the number of eggs we find and move them into the patient’s dish. On average we collect 8-12 eggs per patient, but this can vary. The highest number of eggs from a single patient I have seen is 66 eggs collected.

The egg collection workstation. From right to left we have hot blocks, glass pipette, petri dishes, sterile gloves, and waste disposal bowl. All tasks involving eggs and embryos are performed in the workstations (Class 3 laminar flow hoods).

The sperm sample is prepared at the same time as the egg collection. We utilise fresh and frozen sperm for treatment, produced or thawed on the day of treatment. We assess the pre-preparation sample and use several techniques to optimise the sperm sample for insemination. Ideally, we want to remove the dead/immotile sperm from the sample to improve the progressive motility (sperm swimming forwards).

Sperm cells on a glass slide.

The eggs are then inseminated in the afternoon, 4 hours after egg collection. There are two methods of insemination: IVF or intracytoplasmic sperm injection (ICSI). IVF is the culture of the sperm and eggs together overnight, leaving room for the natural selection of the fertilising sperm. ICSI is the injection of a single sperm into an egg. Whilst we learn how to perform IVF on the STP, ICSI can take months to master, and training typically begins after completion of the STP.

Intracytoplasmic sperm injection (ICSI). The pipette on the left holds the egg in place while the pipette on the right containing a single sperm cell pierces through the outer membrane. The sperm is deposited into the cytoplasm of the egg.

Embryo development – from fertilisation to transfer

On day 1 we assess the eggs for signs of fertilisation. Using various microscopes, we check whether the correct genetic material is present in the eggs. Normal fertilisation is indicated by two pronuclei, genetic material from the sperm and the egg. Any normally fertilised eggs are moved to culture dishes, and abnormal embryos are discarded at this point.

One of our smiley little embryos. The two circular bodies at the top are the pronuclei, indicating the embryo is normally fertilised.

The embryos are monitored by laboratory staff for up to 6 days to assess embryo quality. We utilise standard benchtop incubators and EmbryoScope incubators in our laboratory. The EmbryoScope takes pictures of the embryos every 10 minutes, providing us with a wealth of information on their development and the ability to utilise this data for research purposes. Having the ability to watch the progression of an embryo from fertilisation to the blastocyst stage is fascinating and allows patients to also see the development of their embryos.

On day 5 we perform the embryo transfer. The best embryo is selected by the embryologist and transferred back to the patient using a catheter. As an embryologist, we select the embryo/s for transfer based on development and morphological characteristics. We load the embryo into the catheter and hand it to the clinician in theatre for the transfer procedure. At the end of the embryo transfer, we check the catheter to ensure the embryo has been replaced in the patient’s uterus.

Cryopreservation – freezing little embryos…

The remaining embryos are monitored for cryopreservation. Top-quality embryos can be ‘frozen’ using liquid nitrogen for future use. The temperature of the embryo is gradually decreased using specialised media for cryopreservation before the embryo is placed onto a patient-labelled straw and submerged into liquid nitrogen at -180˚C. The embryos are stored in liquid nitrogen tanks called Dewars, where they remain for many years. Dewars must be filled with liquid nitrogen once a week – no one in the lab team likes tank duty. The Dewars have an alarm system that monitors the temperature and level of liquid nitrogen. A member of the embryology team must be ‘on-call’ in the event a tank fails, and the patient samples must be moved.

Frozen embryos can be thawed out for transfer at the patients’ request. Embryo freezing enables patients to use the spare embryos from their first cycle. This reduces the need for invasive procedures like egg collection and is cheaper than a fresh cycle of IVF. Approximately ¼ of cycles are funded by the NHS, so the cost of treatment is an essential factor for many patients. We perform frozen embryo transfers weekly at the Centre for Reproductive Medicine (CRM), thawing the embryos in the morning before the patient arrives at the clinic. The embryos are monitored throughout the morning to ensure they have survived the freeze-thaw process and will then be transferred to the patient approx. 2 hours after thawing.

Cryopreservation is an important part of fertility preservation. This is essential for oncology patients, those suffering premature infertility, and transgender patients. We routinely store sperm, eggs, and embryos for fertility preservation patients.

So far in my training, I have been signed off on egg collections, sperm preparation, IVF inseminations, and fertilisation checks. The STP can be challenging when trying to balance university, work-based training, and portfolio work. Choosing the right specialism is important, ensuring that you find something that inspires you and makes you want to push yourself daily. Embryology can sometimes be emotionally draining when you consider everything the patient has been through to get to this point, but I find my job very rewarding when we receive positive pregnancy test news and pictures of CRM babies. Each day and every patient is different, and the field is still so new that we’re always able to expand the scientific field and continuously learn something new.

By Laurie-Anne, second-year STP trainee in Embryology, @laurieanne98 (Twitter and Instagram)

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