In this guide
Day by day in the lab
Every clinic works differently, but this is the usual pattern after egg collection (day 0):
- Day 0, collection day: your eggs are mixed with sperm (IVF) or each mature egg is injected with a single sperm (ICSI), usually within a few hours of collection.
- Day 1: about 16 to 18 hours later, the embryologist checks how many eggs have fertilised. This is the update most clinics give you. Not every egg fertilises; 60 to 80% of mature eggs is typical.
- Days 2 to 4: the fertilised eggs divide. By day 3 a typical embryo has 6 to 8 cells. Some embryos that look slow on day 3 catch up by day 5, so try not to read too much into early grades.
- Days 5 and 6: good-quality embryos become blastocysts. Most clinics wait until now to choose an embryo to transfer and to decide which can be frozen. Some embryos reach this stage on day 6 rather than day 5.
Why you may not hear anything
Many clinics call on day 1 with the fertilisation result and then not again until the day of transfer or freezing. Some leave embryos undisturbed between checks, so there is no new information to give you. Silence on day 3 or day 4 usually means nothing has changed in the plan, not that something has gone wrong.
That does not make it easier. Not knowing is one of the hardest parts of treatment, and it is reasonable to want a clear plan for who will call and when.
Agree a call plan before you leave on collection day
Ask these before you go home, and write the answers down:
- Which days will you call me, and roughly what time?
- Who will call: the embryologist or a nurse?
- What will you tell me on each call: how many fertilised, how many are developing, how many are good enough to transfer or freeze?
- If I have not heard by the time you said, what number do I ring, and when is it staffed?
- Is there a number for out of hours?
- When will I know whether any embryos have been frozen, and how many?
- If no embryos develop, how and when will you tell me, and who can I talk to afterwards?
When not to wait: call your clinic straight away
Mild bloating and discomfort are common after egg collection. Call your clinic straight away, day or night, if you have any of these. They can be signs of ovarian hyperstimulation syndrome (OHSS):
- Severe bloating or swelling of your tummy
- Severe tummy pain
- Feeling sick or vomiting so that you cannot keep fluids down
- Passing much less urine than usual
- Difficulty breathing
If you cannot reach your clinic, call NHS 111. Call 999 if you have chest pain or severe difficulty breathing.
Looking after yourself while you wait
Clinics must offer you counselling, and it is there for the waiting days as much as for the big decisions. Ask how to book a session before collection day, so it is in place if you need it.
It can help to plan something for the time you would otherwise spend watching the phone, and to tell one or two people when the calls are due, so you are not waiting alone.
Sources
- HFEA, In vitro fertilisation (IVF) (opens in a new tab)
- NHS, IVF: what happens (opens in a new tab)
- NICE guideline NG257, Fertility problems: assessment and treatment (2026) (opens in a new tab)
- HFEA, Getting emotional support (opens in a new tab)
- MedlinePlus, Ovarian hyperstimulation syndrome (opens in a new tab)
Last reviewed 13 September 2026. General information, not medical or financial advice. Your clinic and a regulated adviser can advise on your situation.