To want to take a 3rd year long maternity leave from work?

[Wintersun]

I would love to have baby no.3 but I keep getting pangs of guilt that I'd potentially be taking a 3rd year long mat leave from work, in 5 years.

I like my work. I've been with them for nearly 10 years. They like me and accepted my request to return part time even though its very rare for anyone to work part time in my line of work.
I work in the City for a large financial corporation.

You're not unreasonable to want it, no. The system is in place and open to you and you would not be 'defrauding' anyone by taking what you are legally entitled to.

It all gets a bit more complicated I suppose when you start looking at future opportunities and your relationships with colleagues etc.

But unreasonable to want a baby, and time that you're entitled to? No, not in my book.

YANBU, although having just done exactly that, and had my 3rd baby in 5 years, the atmosphere and the attitude towards me is very different now . I don't feel that I'm taken as seriously because even though I have said that I will travel if required, or work at home if projects need attention on the 2 days I don't work, I'm not being given the same level of client work or responsibility......

YANBU at all. Yes, you'll feel guilty, but they'll manage without you. Just put it to the back of your mind and go for it!

I'm sure you know YANBU. You are feeling unjustified guilt. As SPARKLE says, the system is in place and you are doing nothing wrong by using it.

I start my first lot of ML next week but (if all goes as I hope it will) I hope to be going on a second lot of ML within 18 months. I'm already wondering how this will go down at work and like you, I enjoy my job and have good prospects. My family will always come first though.