Kristen Jones - The journey of eggs and sperm in the IVFla

Find out about the journey of your egg and sperm in the IVF Lab from embryologist, Kristen Jones from ‘I like my eggs fertilised’.

You’ve injected, stimulated, taken multiple drugs, been internally monitored and had more blood draws than you care to remember. Once you have had your egg collection you may be relieved to know, your hard work is over (for now). And so begins the journey of your eggs and sperm in the IVF lab.

The journey of your egg and sperm in the IVF lab

Step 1: Egg Collection

During your EGG COLLECTION, your follicular fluid is drawn out and taken to the Embryologist for examination. Your eggs are taken out, washed in a special media and put aside to patiently wait in the incubator to meet the sperm later on.

Step 2: Sperm is washed

Meanwhile, the sperm (either freshly produced or frozen, donor or spouse), is washed to remove the seminal plasma and prepared specifically for either IVF or ICSI, whichever treatment the doctor has decided is best for your circumstances.

Step 3: IVF & ICSI insemination

At the time of insemination, a measured concentration of washed sperm is added to each well of the dish containing eggs. This is IVF.

If ICSI is being performed, the eggs are stripped of their fluffy cumulus cells to identify which ones are mature. The mature eggs then get injected with a single sperm. Eggs are returned to the incubator and left for 16-18 hours.

Step 4: Checking fertilisation

The following day, it is time for a fertilisation check. The embryos are observed to see whether 2 pronuclei are visible – a nucleus from the sperm and one from the egg. This is a successful fertilisation.

Sometimes, we see eggs that abnormally fertilise, partially fertilise or do not fertilise at all. Generally, about a 50% fertilisation rate is considered reasonable.

The embryos will get monitored over the next few days. Different labs have different time points for this and you may or may not get any updates. You will be told when to come in for your transfer or you will be told when your suitable embryos will be frozen if you are not having a transfer.


(although different labs may slightly vary)

  • Day 2: 2-6 cells
  • Day 3: 6-10 cells
  • Day 4: compacting to cavitating
  • Day 5: early blastocyst to expanding blastocyst
  • Day 6: fully expanded, or hatching, hatched blastocyst

It’s important to know that not all embryos are expected to be suitable for transfer or freeze.

Step 5: Embryo Transfer

You will be told what day to go in for your embryo transfer and this is a procedure similar to a Pap smear or an IUI. A speculum is inserted to visualise the cervix.

The Embryologist brings in the catheter loaded with the embryo, which is then placed through the cervix and gently displaced into the uterus. It is mostly a quick and comfortable procedure, although some patients do report some discomfort.

Based on multiple factors such as embryo numbers, quality and past results, your team will make the decision of what’s the best day to have your transfer done. This is usually a day 3 or day 5 transfer although many labs do other days as well.

Step 6: After your embryo transfer

After your embryo transfer, you may get more updates from the lab regarding remaining embryos and if anything is suitable for freezing, and then your journey in the lab is done for now. You are now in the Two Week Wait (TWW) as you wait to find out if your transfer resulted in a pregnancy or not.

A lot of patients are very upset to learn that even though an embryo has been placed directly in the uterus, pregnancy does not always result. And unfortunately, even in the best circumstances and with the best embryo, pregnancy is not guaranteed.

Your lab and medical team will do the best they can to make the right decisions for your treatment to give you the best chance of success they can possibly give you.

It’s important you get support – check out all the IVF support materials in Your Fertility Toolbox. and read our 50 top tips for IVF. 

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Kristen Jones

Kristen Jones

Clinical Embryologist


Kristen is an Accredited Embryologist in Perth, Australia. Since doing a degree in Biomedical Science degree she devotes her career to helping other people get pregnant and went on to complete a Masters degree in Reproductive Medicine from UNSW.  After going through her own struggles to conceive, Kristen became passionate about educating about natural fertility and fertility treatment and founded ‘I Like My Eggs Fertilised’ to make it a more positive, less stressful experience.