Why did my IVF numbers drop so much between retrieval and embryo formation?

That kind of drop can be really upsetting, but it’s not necessarily unusual. The biggest attrition can happen at different stages—egg maturity, fertilisation, embryo development, and especially between day 3 and day 5. The fact that you still have 4 embryos on day 5 means you have embryos that made it through an important stage.

It is actually pretty common for numbers to drop at each IVF stage. Not every retrieved egg is mature or fertilises and not every fertilised egg develops into a good-quality embryo. Egg & sperm quality, age, and lab factors can all play a role. It can be stressful to see the numbers fall, but the final embryo quality matters more than the starting number.