FMLA, take prior to delivery / due date ?

First, I am eligible for FMLA (worked full time at current employer for four years).

I have had a very rough pregnancy due to Hyperememis and other health issues that were present prior to pregnancy. At this point I would like to take leave from October 9 – December 22.

My due date is Oct 28. Both of my older children came early. One came 17 days early.

I have read the FMLA govt website but it is not clear. My HR department is not answering my questions and I understand they are looking at the Company’s best interest and not mine.

My question,  can I tell my employer when I am taking FMLA? Or can I only take it once I go into labor? Can my doctor put that he is recommending these dates due to complications?