WFA Timelines near end of pregnancy

Sounds like our department will be sending out WFA letters in January when I’ll be 36+ weeks (9 months) pregnant. How does the WFA process work if folks are on maternity leave after the letters are sent? The stress and anxiety about becoming a new parent is bad enough, but will I be expected to compete for my job freshly postpartum while on maternity/parental leave? Will I have to cut my 18 months of leave short to work?

All tips/guidance is hugely appreciated.