telling the parents

Hi ladies, I'm currently 5w4d with our 4th. 
I'm freaking out about telling my parents when the time comes because they claim they 'couldn't handle it if I fell pregnant again' 😔
I'm 31 damn years old and married, they've looked after 2 of my 3 children a total of 3 or 4 times in the past 5 years, I don't depend on them for much at all really. We don't go out and party etc and I don't even know what their huge objection is to be honest. 
Our house is small but we have plans to renovate (not just because I'm pregnant, it's been planned for a while).
I just really don't know how to tell them when the time comes as it already has me so nervous and anxious 😔
If any of you have been in this situation then please let me know how it turned out. 
Thank you for reading this and sorry for rambling.