Hello,
First of all, please note that the leave that you need cannot be termed as "Maternity Leave". ML is granted to a female employee who is in advanced state of pregnancy or has undergone (unfortunate) miscarriage, with specific ceilings for each. The leave that you require is a normal kind of leave (probably by producing a medical certificate necessitating absence from duty), which is to be treated based on normal leave rules of your organization. At the best, you can get leave with pay to the extent of credit available, followed by leave without pay. Since you are in probation, there is a possibility that your probation may be extended.
I suggest that you convince your management to permit you to be absent for the specified period by providing proper records. If you look from the organization point of view, there will be loss of productivity, extra expenses (to employ a temporary person during your absence) etc. In my opinion, your organization is definitely empathetic towards you and this should be appreciated by you by not extending your leave of absence and rejoining duty.