In vetro question.

So my best friend has been trying for many years to have a baby. She just had her second round of in vetro. Because of medical issues they can only insert 2 fertilized eggs. Well one stuck! We are super excited however.... Today she went in and had an ultrasound at 6 weeks. They said the yoke sac seems inlarged and don't see anything else in the sac. Is that normal? I'm trying to remember with mine I don't think we saw anything till at least 7/8 weeks. She is freaking out and I feel so bad. I want her to be ok. Anyone have this and continue with a normal pregnancy?