Hi Jade, usually the clinic will thaw them one by one, so if you want two put back they thaw the first two, then if one of those doesn't make the thaw, then they'd thaw another one. The clinic knows within an hour or so if the emby is going to survive the thaw. The clinic will confirm your wishes, you can opt for thawing of two and two only even if one or both don't survive. HTH