Blighted ovum

Christina
I went to the doctor to confirm my pregnancy and he did a test there. I am pregnant about 5 weeks and 2 days! Due date is April 2nd, and I have my first ultrasound next Friday at almost 7 weeks. I'm kinda worried about a blighted ovum. The lines on my pregnancy tests when I test keep getting darker which is a good sign but my question is, if my doctor would have suspected that would he have done tests then? Are there any signs? And what are the chances of a blighted ovum now that I have confirmed everything and know the lines are getting darker on tests? So worried. My first pregnancy was a healthy one!