Thank you for all the advice and congratulatory wishes. It's been helpful to see all the different points of view.
There have been mixed opinions but the general consensus is that I can lose my job for being pregnant during the 3 months probation.
After discussing with my OH, we're going to wait until the 12 weeks before we actually tell anyone! Close family included. As mentioned by some, the first trimester can be uncertain, particularly with PCOs and Endometriosis the risk of something bad happening is higher than usual. I don't want the added stress knowing that my parents, as well as, others may be worrying for me. I feel it would be better mentally to carry on as normal.
After the 12 weeks, I should have another 2-3 weeks before my probation ends, during which we will still try to keep it quiet. I can only hope that my employer is not too angry.
Financially, I need to work until the end so we can afford all the extra things. And I feel I will be more than capable to keep performing well and contributing in my role for the next 7 months!
If my employer did decide to let me go now, I would be losing out on 7 months of earning and now that I know I am pregnant, I definitely would not go searching for a new job! Telling them at the end of October gives 4-5 months for my employer to find cover, which I feel is enough time.
If after I have given the news and they react badly, treating me cruelly, then I will likely leave. Yes a new cot, pram and clothes would be fantastic, but, what use is that if I have to face a horrible environment, further risking problems. Happiness and health come first. Our top priority is to bring a happy, healthy baby into this world.
In answer to some questions:
I was not asked during my interview whether I was planning to start a family.
I have no idea whether I will go back to work! Maybe we'll win the Euromillions by April... Maybe my OH will suddenly get a pay rise! Or maybe we'll learn how to spend less and make do with one salary! We'll just have to see how it goes.
Thanks again everyone!