My wife and I know a couple who did this.  At first, it seemed like a fairly innocuous and even slightly charming excuse to have a party.  The more I think about it, though, the more it seems like a rare combination of creepy and self-serving:

This is only one example of the newly ubiquitous, guilelessly documented Gender Cake Party, in which a couple hands over the obstetrician's report to the local bakery, then receives the news in a manner they firmly refuse to acknowledge as symbolic: from a newly sliced, triangle-shaped wound of tender flesh.

 h/t: kottke.org