The mean-spirited cheerleading coach was pregnant in the Fox drama's third season and will have given birth when season four begins.
"I think the thing is, Sue Sylvester is pretty set in stone with who she is," Lynch told The Hollywood Reporter.
"She's your best friend and your worst enemy. When she has something to fight for, she's never better."
The identity of the baby's father is currently unknown, with Lynch speculating as to who could play Sue's former lover.
"Why would I like to work with? Oh, Hugh Dancy. Why not?" she joked.
Dancy - who is the 37-year-old husband of Homeland actress Claire Danes - has been cast in NBC's upcoming drama Hannibal as FBI agent Will Graham.
Glee will return for its season four premiere - titled 'The New Rachel' - on September 13 on Fox. In the UK, the series airs on Sky1.
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