Are Baby Showers Supposed to be a Secret?

Ke
Everyone I've spoken to seems shocked that I know about my baby shower and that it's not a surprise. I didn't realize it was so common to have surprise baby showers.  I personally like knowing because that gave me time to shop for a dress and I formed a lot of my to do list time line around the babyshower date.  Are baby showers supposed to be a secret from the mother to be?