Your concept seems quite interesting with a lot of potential for scares, but I'm struggling to follow the logline.
"A three month pregnant healthcare worker"
This feels a little too detailed. Is it essential that we know how many months? Consider "A newly-pregnant" or "An expectant mother". I think you can omit "healthcare worker" since that's implied in the next phrase, but that's up to you.
"grim shift"
'Grim' is a good word, but it might be more powerful placed elsewhere. Is the shift grim to begin with? If so, what makes it grim? Consider "An expectant mother's shift at the psychiatric hospital turns grim when..." -- this way the shift starts off normal.
"a possessed patient wants her in horrific fear"
This phrase isn't grammatically correct. Can you clarify what the possessed patient is doing / desiring?
"at the sight of the demonic being that lives inside her."
I'm also a bit lost with the pronouns here - so far, the only "her" we've had is the psych worker. Who is seeing the demonic being? Who does it live inside - is it the baby?
Another aspect to approach is this: what is it about your story in particular that makes it different from other supernatural horrors? Can you capture some of the Act II conflict in a few words?
My take:
"An expectant mother's shift at the psychiatric hospital turns grim when a possessed patient makes an attempt at her life - and the unholy life of her unborn child."