Welcome to the site.
To have 2 normal pregnancies then PE in the third is very rare but as you will know, can still happen.
Often there are underlying markers in the previous pregnancies that might have developed into PE had baby not been born so it is very much worth a close look at all the pregnancy histories.
Usually, babies born close together (within 2 years) offers some protection against PE. Equally pregnancies 10 years apart have a higher risk of developing PE.
The following is an abstract from a study which shows some of the statistics which might help.
Among women without pre-eclampsia in their first pregnancy, the risk of pre-eclampsia was 0.83% if they became pregnant again within two years and 2.2% if they became pregnant more than eight years after their first pregnancy; the corresponding risks were 13.1% and 15.8% for women with pre-eclampsia in their first pregnancy
My suggestion to you Mark would be to seek the opinion of a specialist consultant to go through all your wifes pregnancies and look for the underlying markers if possible to plan your care and risks should you decide to go ahead.
If you would like to talk this through then I am available from 11am-3pm Mon Fri on 0845 2410989?
I hope this helps.
Every Woman is entitled to understand what happened in her pregnancy when pre eclampsia strikes. I hope to be able to support that process.