Colts Star Antoine Bethea -- Gives Pimped Out Ride As Baby Present

Some guys give their wives diamonds when they give birth ... but Indianapolis Colts player Antoine Bethea just set the bar even higher ... lavishing his fiancee with a super tricked-out BMW.

Antoine tells TMZ ... he bought the 2013 BMW X6 to celebrate the birth of their daughter (that's called a push present, guys) and his fiancee's birthday ... then had the whip completely rebuilt.

Sources close to the customizing shop say the car has about $30K worth of modifications, including:

-body lowered 3 inches
-custom grill
-smoked head and tail lights
-customized bumpers
-powder coated black rims

And the sickest part of all ... lighted projectors in the doors that project the BMW logo onto the ground when the doors are open.

BMW. The ultimate birthing machine.