In your case, you have agreed to start work at a new company and the agreement therefore becomes binding and creates an employment contract between you and your employer. Therefore, your employer must treat you like any other employee. So it does not make any difference that you have just joined. Even if your employment contract contains a probationary clause in it stating that your employment could be terminated in the first couple of months, this will be related to your job performance and again if your company tried to use this probationary clause to terminate your employment contract due to you being pregnant then they would potentially be breaking the law.
You do not have to tell your employer that you are receiving fertility treatment – that is your call. Some employees might rather tell their employer upfront so their employer can be more flexible and understanding when time off is needed for doctor appointments.
Finally, if you do become pregnant, you are entitled to Statutory Maternity Leave of up to 52 weeks – there is no qualifying period for this. However in order to be eligible for Statutory Maternity Pay (SMP), you will need to have been employed by your employer for 26 weeks in the 15th week before the baby is due.
All the best – good luck.
Whilst every care has been taken in compiling this answer, WorkingMums cannot be held responsible for any errors or omissions. This information is not intended to be a substitute for specific legal advice.