The thing is, you simply have no idea what it's going to be like, first time round.
You would be foolish, I think, to plan to work during your maternity leave, because you could be putting undue pressure on yourself.
Yes, some women (as is evidenced on this thread) manage it, but lots don't. And you haven't failed if you don't!
Babies are hard work.
There are three key things to think about here:
First, you don't know if you're going to get a baby that sleeps all day/night, or one that's colicky (surprisingly common - and you will find it very hard to put a colicky baby down or leave him/her alone if they're suffering.)
Second, don't underestimate the physical impact that giving birth can have on you. This, plus lack of sleep (most new babies do not sleep right through the night, so you'll have to get used to waking several times a night) can leave you sleep deprived pretty quickly. You aren't going to feel as on top of things and ready to tackle your work like you might normally.
And thirdly, your maternity leave is time for you to get to know your baby!
If you can afford childcare, I'd definitely recommend this. It's the only reliable, guaranteed way that you'll be able to work with a baby.