About a week behind?

Clare

Hi! I’m just over 10 weeks pregnant after my fourth round of IUI. I had a scan around 8.5 weeks and the DR said the baby seemed about a week behind. She said that she wouldn’t be concerned if I wasn’t IUI and I’ve another scanned booked for next Monday. I am struggling to think of anything else but what could be wrong! Has anyone been through anything similar?? All advice welcome.