I saw an article once in an obstetrics journal about the average IQ drop for women in their 3rd trimester. It was significant (10-20 points,, I think). The point of the article was that even bright women will require different educational materials when they are "impaired."

My baby is 12years old and I'm loving it. I have never once looked back or been nostalgic about those first 5 years, but I have never been a baby person.