Blighted ovum?

A

Can someone please tell me about blighted ovums? Should be about 7+ weeks, went for 1st appointment/US today and doc saw no fetal pole. The sac measured correctly at 7 weeks. This would be my 3rd baby so know at this point there should be an embryo and heartbeat. I’m assuming this isn’t going to end well but not sure what to really expect from here.