Many many things about announcement cards
The design you should choose therefore should speak your sentiments and joy. Since definitely you want a picture of your baby in your card, the design that you choose therefore should match your picture. For example, you can choose a sports theme if your baby is in his infant sports gear. Or you can be more formal and choose a design that suits your baby's tiny bow tie. Whatever you choose, formal, sporty or any theme, it will surely be a token of this moment of your life as a parent.