Hi Louise,
If your boss is really trying to get you out of the company suspecting that you are pregnant, I would officially tell him ASAP that you are pregnant! The reason is that it is unlawful to fire someone on grounds of pregnancy (it is called discrimination on grounds of sex, as it is a gender related condition) and once he knows, there is not much he can do, apart from paying you maternity leave if he does not want to end up in court.If you do not tell him that you are pregnant, he can always make excuses and say that he did not know that you were pregnant and that he laid you off because of i.e. incompetence, so if your suspicion is right, hurry up and tell him.
To Caroline,
You may not be entitled to maternity pay but your employer do have an obligation to take into consideration you condition and adjust your work load accordingly. I don’t know how big your company is, but if there is a Human Resources department, I would go and speak with them about this.