I asked my RE the same question after my last IVF cycle. She said they are alomost the same and studies done did not show one to produce more pregnancies than the other.

I had read that 5 day was better. But I think they really want to get them back in us sooner than later. Also, sometimes they stop growing after 5 days. I think they wait 5 days if they are not developed good enough by day 3 and also if they are watching for abnormalities.

But a few places just prefer 5 days now. Most common is 3 days.

Hi LP, this is what an RE told me on another site. Some clinics have more experience and success with 3 day, other 5 day. Some do both. If you have lots of good embies, they might have you go to 5 day. If you don't they will do a 3 day as the embies often do better in you than in a dish. Rates for 3 versus 5 are similar, but multiple rates for 5 day are less. So, in a perfect world you would do a 5 day so that you would have less of a chance at having multiples.