You would have no legal, automatic right to remain in the U.K. You would need to return to your home nation at the end of your visa. Even marrying the father would still leave you in the position of having to fulfil certain criteria to remain in the U.K. If you give birth in the UK your child can remain with his or her British National father.
Secure your citizenship before bringing a child into the equation would be my sincere advice. The immigration and citizenship procedure in the U.K. is long, harsh and unkind, don’t make a child suffer through it if you can avoid doing so.
from Quora !