Clara I found work became very difficult towards the end. I work in a busy clinic and had no allowances or breaks (which you are entitled to)
For this reason I finished a month before my due date.
Don't forget that you are entitled to all of your annual leave for that year, so I used this for the first three weeks, which meant my maternity leave officially only began a week before my due date. I enjoyed that time off, buying baby things, washing baby clothes and generally relaxing. You won't have that chance with your second maternity leave.
One thing to bear in mind though: if you do use annual leave to finish early, and your baby is born during this time, then your maternity leave must start on the day baby is born. So unless your employer is generous and allows you to carry over the lost annual leave, then you lose out.