Hi Mrs Mopp
Firstly, congratulations!
If you just let your Trustee know about this change and what you are planning (having to live on maternity pay or not etc, ie how this will affect your income etc) and how they want to handle it.
You should be able to put your monthly contributions on hold for a while until you are able to get things back to a bit more normal. This will mean your Trust Deed would last longer but I would certainly ask them about it if that would help.
As long as you show the willing to co-operate and be honest you should have no worries. And they have NO say in how you live your life - only your finances etc for the next few years - don't you worry.
Best of luck and let us know how you get on.