Getting anxious about telling work mat leave etc...

I am 8 weeks pregnant tomorrow, it's been a rollercoaster already, some of you may have seen a previous post of mine about deciding to keep and what to do in unplanned pregnancy.

I'm still massively uncertain but climbing tentatively on board the baby. I need to tell my boss fairly soon, the work I do involves teratogenic compounds and although we can greatly reduce risk my partner has asked that I removed the risk completely.

I have only been working for the company for 3 months, I have my probation meeting next week and I am hoping hoping I can push telling my boss into next year January when i have passed probation. I am really anxious about telling them, I don't know how to bring it up, how to make it feel like a safe space for me and how to in all honesty apologise. In my interview I was clear that I wanted to stay in this company and make use of progression opportunities and this has sort of put a spanner in the works! I'm on a 15 month contract with the company itself which makes me a normal employee, that I hope they will extend they explained this was likely at interview and application... but I will be a bit ruined if they don't.

I have had great feedback on my work so far and I'm trying to believe that this won't impact me in the long run and I know that it shouldn't but that doesn't mean that's a guarantee.

Essentially: How do you tell? Do you think I should say that it was unplanned? Do you think this will mean that they don't extend my contract?

Also weird one, how does normal AL work with mat leave? I'm wondering if I can spread my AL across mat leave so it increases the pay a little in months when I'm moved to statutory.

TIA