I have also been told I have low platelets, although I am much earlier on in my pregnancy. I saw the consultant a few weeks ago and she said it would only have any bearing on the birth if the levels dropped to 80 or below, in which case I would not be able to have an epidural or c section.
I'd get your wife's midwife to seek another opinion if she isn't sure.
I doubt if they drop any lower that your wife would be allowed a home birth. Of course she can still have one but it would be recommended against. Below 80 is no epidural, below 50 is a transfusion at some hospitals. However below 150 means an increased risk of bleeding. X