Should I tell?

I'm in a bit of a predicament and want opinions. My oldest sister is pregnant with her first child and she's due in May of this year. Keep in mind that she's almost 40 and already established. (Naturopathic doctor, married, owns her own clinic, etc.) I found out I was pregnant a little over a week ago and I'm currently 6 weeks and 6 days in. My question is should I wait to tell her until after she has her baby or go ahead and tell her? I'm 22 and this is my first child also but I don't want to feel like I'm taking a special moment away from her. I haven't even told my parents about it yet. Another reason I'm debating on whether or not to tell my immediate family is that I'm "the baby" of the family and I'm not yet established. I live with my fiancé about 1,000 miles away from our parents and we've been together for almost 6 years. I know that I'm a grown woman and that I can still accomplish my life goals while taking care of my child but I don't want them to worry or have anything negative to say.