Hi,my friends 2 months pregnant and starting a new job but her previous employers know she's pregnant but her current employers don't know yet,will they put it down in her reference? Cheers

It should not come up but there is no guaranttee that the old employer will follow the rules. Employers can fail to follow the rules in 2 main ways; intentionally or by mistake.

Normally no, unless there was a medical issue such as being fit for certain work where it could be an issue