I will go back and read the whole thread, but I thought I'd add my experiences first.
I have worked at the same company for eight years this summer. Last year, I was approached about applying for another (better) role, I ummed and ahhed, but given DH and I had been TTC for 2years, I knew that (hopefully) sometime soon I'd be on maternity leave again. I declined to apply. I was then approached again by the managers asking me why I hadn't applied, so I was very honest and said that I was TTC and would prefer not to be in a new role, they told me that it wasn't an issue and I should apply, so I did and got the role. I found out I was pregnant on my first day in the new role. Not an issue, boss was lovely about it.
A few weeks later, another role came up, again a step up the ladder, in my old team, one that I did not think would be opening anytime soon. I again ummed and ahhed, but stuck in my CV, and had a chat with the hiring manager before hand, and did say that I was pregnant. I was still hired, started the role in Dec and am due to go on mat leave in May. They are very supportive.
I accept that the company may be quite forward thinking, and in no way did I ever have to tell anybody that I was TTC but I wanted to be honest with them about my intentions.
In my case it may be slightly easier because I have been there for a long time, so not a new role in a new company, so I have a "track record" iyswim (won global employee of the year last year). Whether i would be so honest if applying for a different company, I dont know. However, I'm now also honest about the fact that this (being my second) is going to be my last baby, I don't plan to get pregnant again.
Off to read the rest of the thread now.