My Wife Had An Iui On The 11 Th Of

My wife had an iui on the 11 th of september, since then she was on Folg1 and ecospirin tab, also she had been given vageston to be used twice a day. Today is the 18th day after IUI, and we did a pregnancy test using test kit, which returned negative results. Usually she has her periods three days in advance, where she had her last one on the 1st of September. I therefore want to ask, is it normal for her to have delayed periods, or there is some thing to worry ?