Why do moms in the UK do this for babyshowers?

How it works: Guests with babies all bring in a dirty diaper from their kid and put them on a table with a number. Then, all the guests there vote on which poop looks the "best" (healthy, full, etc). It's supposed to bring good luck or something to the mom to be, but to me it just sounds disgusting. The fuck is wrong with you Brits?