What it means

Fertilisation rate refers to how many mature eggs successfully combine with sperm to begin developing into embryos. It shows how many eggs move forward after the fertilisation step.

When it’s used

It’s discussed after egg retrieval and fertilisation, usually when the lab gives an update on how many eggs have fertilised. This is one of the first major updates after retrieval.

Why people get confused

Many people expect all mature eggs to fertilise. But this is not always the case. Some eggs may not respond, even when sperm is used or ICSI is done, so the number often drops at this stage.

Think of it this way

If egg maturity is about which eggs are ready, fertilisation rate is about how many of those ready eggs actually start developing.

What to expect

You may hear numbers like “10 mature eggs, 6 fertilised.” This drop is a normal part of the process. It is one of the early points where expectations and actual results may start to differ.