Maternity leave through FMLA

Will your employer let you start your leave before you give birth? At my job Maternity leave doesn't start until the baby is born. But only 6 weeks is Maternity leave and the other 6 weeks is just FMLA. I was wondering if I could split up the FMLA. My due date is January 10th. I was thinking about just not coming back after New Years but if I don't go in labor by then i'm not sure if my employer will let me. How does it work at your job?