That depends what you mean by "in the baby's interest".
(And who could possibly be the judge of that?)
If it's a termination for medical reasons then yes it's legal, but even then, depending on what the medical reason is, it might be that the baby could potentially live a fulfilling life if it had the chance to be born, but the parents aren't prepared to take care of it. (Thinking of Down Syndrome, for example. There are enough people out there with Down Syndrome who will tell you that their lives have value.)
In some cases it could also be argued that a healthy baby might be better off not being born for other reasons, and that's a much more controversial argument. If an unwanted child is born to unsuitable parents, placed in foster care at birth and goes on to live an unhappy life, they might argue it would have been better never to have been born. But who on earth can be the judge of that?
I actually became much more strongly in favour of abortion after spending some time volunteering in an orphanage and seeing what happens when large numbers of unwanted babies are born (in a country without easy access to abortions). As lovely as those babies were, I do actually believe that in many cases they would have been better off not being born, and yet...I don't know...the idea of them being aborted at full term still seems completely barbaric.
So yeah, I guess there are some circumstances where I'd say it is not in the baby's interest to be born, but they wouldn't fall within the legal exemption for late abortion on medical grounds.