neverbroken sending you 
I’ve been there. My son was 28 weeks but severely growth restricted so the size of a 24 week baby. We were in for 100 days.
For the benefit of those saying life is not fair....
I’ve found over the years it is just impossible to explain to people. It’s not just that your child is sick and you are living hour by hour, expecting them to die at any minute, surrounded by people who are in the same situation, witnessing ours and eachother’s children going through barbaric procedures, which are necessary to keep them alive (neonates cannot always have anaesthetic, as that in itself can kill them).
But that you then get in a car and leave them to drive for an hour or so to get home and resume your 2-3 hourly pumping schedule throughout the night, call the hospital to check they’re still alive and then get up and start again.
It is extremely common for ex premature babies to have additional hospital time /operations through early childhood.
Indeed, I took unpaid parental leave and unpaid annual leave for that. There is a mechanism in place for that.
It is also vastly more common for ex premature children to have developmental delay and learning disabilities.
But within all of that, the OP is asking about additional UNPAID mat leave.
YANBU
This is doable, it is a defined period. It is unpaid.
Yes, I agree that additional mat leave should be given to parents whose children were in NICU and HDU during the period of mat leave. Covering those parents whose children were born at term but were extremely sick.
By the way, I can assure you this was nobody’s “life choice “ as one poster so considerately put it.