Do you have a specific concern? Is it due to having a 4th, or due to being over 35? In either case, if you are happy about it, then typically others will be. Your body, your family, your life. I say huge congrats to you!!
I am 38 and have 3 boys as well and currently 13w, it was hard at first telling people. My mother will not even talk or ask about the baby makes me sad but hopefully she will come around! Hang in there!!