I NEVER would have considered that, when I had my older DC's.
I did what everyone else did, and wedged the door open with the pram. Strangely no women were interested in peering in at me weeing, nobody stole my children, and I didn't suffer anything fatal by having to have the door open a bit. 
The idea that having a baby is in ANY way comparable to being UNABLE or UNSAFE to use the ladies loo is staggeringly breathtakingly entitled, to me.
You don't become disabled because you have had a baby. It doesn't suddenly stop your arms, legs or brain from working. I can't see why mums are acting like it would be horrifying to leave the door slightly ajar when they use a public loo, or leave their baby in their buggy outside the cubicle.
How do you think your own mums used public loos? Either they had bladders of steel or they left you outside...Christ, I'm only 31, and when I was little people didn't even take prams into the shops, they left the prams and babies outside.
Do you REALLY think that having a baby means you should use the disabled toilets?! REALLY?!