What are the chances of having a blighted ovum twice?

Certainly possible. It would be difficult to give you a number or a percent chance. Blighted ovums and early miscarriage are just very common. Unfortunately it can happen again. Assuming you have no medical issues though a normal healthy pregnancy is statistically more likely.
Recurrent Miscarriag. The risk of a first miscarriage is usually quoted at 15% but the risk increases with maternal age (30-60% over 40). The chance of another miscarriage increases from 15% to about 25-30% for the next pregnancy. On the flip side - thinking positively - the chance of success is very high 70-75%. A single miscarriage is common and most couples go on to have a normal pregnancy.