I can only give you my own person experience, but a very similar thing happened to me recently. I had a scan at 8+3 and baby measured 5 weeks, there was a fetal pole, but very small, nowhere close to what it would be measuring at 8 weeks. I also have a retroverted uterus, but that should make no difference. A retroverted uterus can make it tougher to do an abdominal scan, but they should be doing an internal scan to date anyway at that point.
There is always a chance with these that your dates could be off, but if you know your dates (I knew mine exactly, and actually had gotten a positive test 5 weeks before, so there was no chance I was only 5 weeks pregnant), unfortunately, I'm sorry to say, it means that baby has stopped growing. Your hcg levels will still be high and could even increase as your body believes things are moving along as they should even when they aren't. I had a d&c 2 weeks ago (6 weeks after baby stopped developing) and even now 8 weeks later, I get a positive on a test. It's not accurate. It's just a weird thing your body unfortunately does.
They will have you come back in for another scan though in about a week or so just to check again as they will want to make sure they are giving you the right information. And then they can talk to you about what your options are for moving forward and what you want to do next. That's not to say to completely lose hope, but if you know your dates, it's very likely unfortunately that the scan is accurate. In the meantime, hang in there and take care of yourself. It's such a tough thing to go through, especially when you're hanging in limbo like this. I found that one of the most difficult things, just not knowing what was happening. I found talking to other ladies who had experiencing the same, including several close friends, was really helpful.
