If you are a mother, how was your job performance been affected upon your return from maternity leave?

I am currently a student writing a paper about maternity leave and would like to know how mothers deal with going back to work after taking maternity leave. Did anyone find it difficult to readjust? Did you have a lot of catching up to do? Or did you not take the maximum of 12 weeks of leave? If so, why not? Tell me your stories!If you are a mother, how was your job performance been affected upon your return from maternity leave?
I took 12 weeks off with my first child, my daughter - 2 weeks before I was due and 10 weeks after she was born. It was very hard to go back to work. It seemed like I was always completely exhausted and somewhat out of it, but I managed. It was also really hard not being with her so much when she was so little. With my son I decided to take about 6 months off. That was a much better decision although it was a little difficult financially since I wasn't paid for time off. Even now, with my son being 19 months, I'm still frequently very tired at work since he doesn't sleep through the night yet. I don't feel I'm back up to the mental capacity I was before I had my first child, and maybe I never will be. --I'm in Kansas City, Missouri, USA.