Paulina Gretzky & Dustin -- We'd Be Pumped ... If Our Fetus Turned Pro!

It's got all the right genes ... a PGA dad and an NHL legend grandpa ... but are Dustin Johnson and Paulina Gretzky hoping their fetus takes up golf or hockey??

The newly engaged -- and newly pregnant -- couple were out at LAX yesterday when we asked ... if the kid goes pro in a sport -- are you hoping it picks up the clubs or the sticks?

You can tell Dustin's excited about his baby on the way -- but when we asked about the due date, he wouldn't get into specifics.