thank u for your prompt reply to my e-mail :-) It is a releif to read your reply as round the 3rd time passing urine I had some light spotting and this happened when passing urine a couple times later.
I do not know what this could be but if there was any bleeding during the embryo transfer, it could have come from that. Embryo do not fall out after embryo transfer but bleeding can occur from the endometrial lining or the cervix when an embryo transfer catheter is inserted.