Termination while on STD

The terminal I work for is in PA but the corporation is out of CA (if that matters).

I am in the process of getting Short Term Disability. My physician has me off until at least the end of the year. I know STD usually covers 12 weeks and then would roll over unti LTD for the remainder of time my physician wants me off of work. I am pregnant, high-risk with several complications and risk to fetal loss.

My question is: IF my employer terminates me while on STD am I still able to transition to LTD? Does my termination terminate my disability? I am not eligible for FMLA with my employer.