Telling my boss

I am so nervous to tell my boss that I am pregnant. I have worked there 11 years and this is my 4th pregnancy. I work for a dentist and finding someone to replace me for maternity leave is NOT easy. There is another girl who is pregnant and when she told everyone I saw my boss roll his eyes and sigh. My boss is really a good person but I don’t know how I am going to tell him. Please help give me some confidence and ways to tell them. I want to tell him and my office manager that I know how annoyed they were when the other girl told them and i hope they don’t feel the same way about my pregnancy. That I know it is difficult but in the end it’s what my husband and I want for our family. Is this being too rude? Should I just tell them and ignore their hurtful eye rolls?