The actress - who has adopted South Korean tot Naleigh, nine months, with husband Josh Kelley - admits she would love to expand her family further but thinks adopting again would be better for the world.
She said: "Maybe we`ll have four or five kids. We`ll see how two go. Two could throw me right over the edge.
"We`ve talked about biological children, and we haven`t ruled it out. But I would like to adopt again. It`s a little bit hard for me.
"If I have a biological child, is there a child now who will go without a mom?"
Katherine toned down her heavy work schedule so that she could spend more time with Naleigh, and has no regrets about it.
She added in an interview with USA Today newspaper: "I can`t cultivate a relationship with my child if it`s between takes. I can`t imagine my life without Naleigh or not being her mother.
"I`m a sappy mom now. I didn`t think I would be. I thought I`d be a cool mom who keeps everything in perspective."