If one relieved himself b’emtza haperek (for example, in Birchas emes vetatziv), and he is concerned that he may need to relieve himself again after davening, can he say Asher yatzar b’emtzah haperek ?
Thank you for your question.
The Mishna Berura discusses a similar case. Does one say a bracha when hearing thunder or seeing lightening? If the person waits until after Shemona Esrei he may no longer say the bracha? He brings different opinions about this, but it seems that he would say not say the bracha. Therefore regarding other brachos that can’t be said after davening, such as the bracha on seeing a rainbow, or in your instance, when the time for saying asher yotzar will pass, because by the time he is finished davening Shemona Esrei he will need the bathroom again. He should still wait and not say the bracha. If he does say the bracha he does have poskim to rely upon, but essentially he shouldn’t.
M:B 66-19, Bais Boruch on Chayei Adom 20ftnt. 28, Eishei Yisroel 19-10, PIskei Teshuvos 66-7.