Trying to determine the answer to this question, A doctoral candidate presented the findings of his experiment to the graduate board.
"I had five couples have sex in exclusive positions, while she was ovulating, to maximize the chances of pregnancy."
"And you're results?"
"Well, we had success in 3 out of 5. The doggy style had a boy, the woman on top had a girl, the missionary had twins- a boy and a girl."
"And the failed couplings? What happened there?"
"Well we didn't have any success with the anal and oral sex couplings."