OK, for what it's worth, this is what I would do. Tie them down re the working from home first and get it in writing. Otherwise, it's always going to be a carrot and you're going to be reticent about addressing stuff that you think needs addressing (flying being the most current example, but I'm sure more will come up in the weeks ahead).

If they get squirmy, just ask them what is going to change between now and your maternity leave that will affect them making a decision on you working from home. That is, there shouldn't be too many variables - presumably the workload can be anticipated along with the type of work. So you can either do it from home or not. Perhaps approach your HR department for advice.

Then sort out the flying business according to what suit your needs best (not what suits the company - I know it's hard, we all want to do the right thing but you need to be selfish in this situation). I'm much more logical about this stuff now after having a miscarriage about 18 months ago which I partly put down to trying to do too much.

So, if you're happy with the cut-off points that the airlines give, use those as evidence. If the airlines' cut-off dates are actually later than you would prefer to be flying, get a doctors' (or obstetricians') note and use that instead.

This is incidental information but my workplace requires a doctors note if I want to work past 34 weeks.