"Three pregnant women at lunch...." joke

Three pregnant women are sitting in a cafe having lunch, when one
of them says, "I know that I'm going to have a boy."
The other two women think about that for a moment, and then one of
them says, "OK, how do you know you're going to have a boy?"
"Well, when the child was conceived," says the first women, "I was
on top. So I'm going to have a boy."
They sit and eat for a few minutes more, and then the second woman
says, "Well, I'm going to have a girl."
"OK," says the first one, "how do you know you're going to have a
girl?"
"Well, when my child was conceived, I was on the bottom. So I'm going
to have a girl."
They sit and eat for a few minutes more, the third woman obviously
getting more and more distressed, until finally she breaks down into
horrible sobbing?
"What's wrong, what's wrong?" the first two women ask with concern.
The third woman manages to stifle her sobs long enough to only say
one thing...
"I'm going to have a puppy!"