I've been lurking ever since I got my really high betas, expecting to find twins in there. I'm 6w2d and had my first ultrasound. There were two sacs, one with a perfect baby and HR, the other one appeared empty. On the screen the empty sac looked very tiny, but it measured 6w0d. My RE said that it is underneath/behind the other sac, so it could just be the angle that made it look empty. She also said that there is a good chance it is a vanishing twin.
Anyone have similar experiences? Thanks!