Blondes and pregnancy

Two brunettes and a blonde are having lunch at a cafe, all three are pregnant. Through out the coversation the topic of sex and pregnancy comes up, finally culminating in each one discussing their respective fetus' and the manner of conception.The first brunette says "I know I am going to have a boy because I was on top." The second brunette says "I know I am going to have a girl because I was on the bottom." The blonde is silent, she has a stricken look on her face, finally she bursts out "Oh my god, I'm going to have a puppy".