It's a bit of a tough call.

I am an employer myself. I would hate it if I employed a person, trained them all up and then discovered that they were pregnant the whole time - and never told me.
It is expensive to hire a person. And a lot of hassle. Setting up workcover and superannuation and taxes.

Also... there is someone else applying for that position who is wanting that job for the long term. Who can give the job 100% now and in the future. And if you were to get the position - they miss out.

And you will not be sure about your morning sickness. With both of my pregnancies... the morning sickness knocked me about so much - there was no way I could have even driven to work - let alone do any work.

Having said all that... if you tell them that you're pregnant right at the start - they can decide whether to take on those responsibilities or not. But my guess is that they wouldn't. And you would miss out on the position.

If I was pregnant, and looking for work - I would be joining an agency and getting temp work. It pays better, and you can have breaks whenever you don't feel so great.