Pregnant for job interview

Do I disclose my pregnancy and openly talk about with my future employers? 
Do I try to hide it the best I can (between 18-20 weeks)?
If asked about it, first, do I tell them that legally they cannot ask me this question, or answer it?
Please let me know if you have been in a similar situation and what ou would do, without jeopardizing the chances of getting hired. Much appreciated.