I think the only expectation for having children comes from parents and if they know you don't want any then I don't know what other sources there could be. Most people couldn't care less if you have a family or not and it's not even something they would think about, most people are far too wrapped up in their own lives.
Well, in all honesty, it sounds like you have no idea, really. Pressure can come from parents and extended family, yes; I mean, I’m the first female on my mum’s side of the family to not have a teenage pregnancy. But the pressure didn’t come from there.
It came from employers asking me when I was planning to have a baby as they didn’t want to take me on if it was going to be soon. Bear in mind that none of my male colleagues have ever been asked this in a job interview, I have been asked in most of them.
I don’t know if you’ve noticed, but people don’t ask if you’re going to have children, it’s “when?”, “how many?” etc but never IF.
Culture presents the women having babies thing as the norm; you may not notice, but maybe you’re lucky in that it doesn’t affect you. I appreciate that there are different societal pressures for different groups, but don’t deny that my pressure doesn’t exist.