To be honest Char, you don't really need it before. You only need it so you can claim the relevent Maternity Pay/ SMP from your Employer/the Government and they don't process it before 24 weeks, so before then its worthless having.
I can kind of see why, as someone who has experienced first Trimester miscarriages, I would have felt a fraud having Maternity leave and pay after each miscarriage as I recovered quickly physically and needed to go back to work to recover emotionally. But I suppose this is going to be one of those things that people feel differently about.
As an employer I'm sure they would be well peeved if everyone who ever got pregnant could claim Maternity benefits regardless of outcome.