Am I right to wait to tell my family?

Me and my boyfriend are expecting our first child, and although we're scared we're excited :) The only thing is my eldest sister is due with her third baby in two and a half months and I just feel in fairness to her we should wait till her baby is born until we tell everyone about ours. I don't want to take the 'limelight' or attention of her baby... am I right to do this?