So my sister is 15w2d we went to her first ultra there was clearly one baby with one sac. We went for a gender ultrasound today and now there is 2 sacs but we still only see one baby! I know is super super rare but do you think it's possible that she got pregnant while pregnant? Or more likely the doctor just didn't see the sac the first time? We're freaking out waiting for the doctor to call back, any thoughts?