Telling family??

Okay, I'm in a sticky situation and really need advice. I'm about 4 weeks along & my husband and I want to wait until we go to the doctor for bloodwork before telling anyone. Problem: my sister works at my obgyn so she will know if I go, my primary doctor is my cousin, and I work at a hospital so my fellow employees would know if I did it here. Help!!! What do I do??? I can't just tell my sister and not tell our parents first, but I want to be 100% sure before I tell anyone. Thoughts???