If your iud came out then its possible that you wouldnt notice that .However,if its in the uterus
then it definitely should be seen on xray or ultrasound
.If indeed its in the abdominal cavity then also it should be seen by xray/ultrasound.Ideally the iud should be taken out for a pregnancy
to be successful.There can 2 scenarios:either its fallen out or its in the uterus or the abdominal cavity.Since you are pregnant,xrays should be avoided.But do another detailed ultrasound with a radiologist
and see if it could be in the abdominal cavity or embedded in the wall of the uterus.If not found,you have to assume that its fallen out.