Civil service - help with understanding maternity policy

[TeaAndBizcuitz]

I've been offered a post with CS (SEO in central gov dept if makes any difference) and I am having trouble understanding their maternity options. I likely won't start for another month or so.
I am not pregnant currently but would like to have a child in the - hopefully - not too distant future. However we have a big mortgage and bills so I want to try and wait until I would qualify for the enhanced pay (26 weeks full pay).
I've read so many variations but the thing I am seeing most commonly is "52 weeks service" but with not much fuether context.
Does this mean you need 12 months service before: a) you go onto maternity leave or; b) the qualifying week (usually 15th week of pregnancy or; c) you get pregnant

You have to have 52+ weeks service by your qualifying week, so by week 25 of pregnancy

For the civil service, it's 12 months by the 15th week before childbirth. So you need to have worked there for 31 weeks before finding out you're pregnant (if you were to find out that you were pregnant at 4 weeks). Essentially, if you work there for 8 months before you fall pregnant, you'll get the full whack.

The qualifying week is not the 15th week of pregnancy, it’s the 15th week BEFORE child is born, so 25 weeks

Thank you all, super helpful