Had dating scan today and was supposed to be 13 according to LMP which is a load of rubbish, I thought about 7 weeks. But scan showed a small empty sack, no yolk even. And that was on an internal. Sonographer said not to worry it looked healthy just too early to see anything else. My research suggests sack is 5 weeks, so I go back 2 weeks. But I got first BFP (very very early) 4 weeks ago. Almost impossible I thought, but sonographer said it wasn't uncommon still (maybe she was being nice). Anyway going back next week for another scan. Just wondered if anyone else had anything similar happen? And if it's a blighted ovum, what should I ask / expect to happen?