How to hide pregnancy at work?

I work with a pretty awful team of ladies who I KNOW will use my pregnancy against me if they knew. This is my second so well have 2 under 2, and they already throw me under the bus for missing work because of my husband or son, who are my top priority. I do NOT want to tell them I'm pregnant, even though I'm so excited about it. I gained weight as soon as I stopped nursing, so I feel like I already look pregnant and I'm only 12 wks. Any suggestion on how to hide my little miracle? Or how to respond or defer the conversation??