I don't suppose you've got a cite for the central claim here? It's a decent enough example of reasoning from the bottom line whether or not it turns out to be true, but I Googled a couple different sets of keywords, and the only thing that came up besides a whole mess of birth records and obstetricians' papers was Warwick's lecture notes.
This paper is my best lead so far, but it's behind a paywall at the moment. I think it's in "Bayerthal (1911)", whatever that turns out to be.
Here's another installment of rationality quotes. The usual rules apply: