I've tested it. It doesn't always work. I would guess a 75% chance of one you're aiming for and a 25% chance of the other with both the strawberries/carrots and listening to pop/alternative. Probably would have to stay on the same lot for the entire pregnancy doing one and/or the other method for a higher chance. That means no other food and don't leave the room with the music for the entire pregnancy. So no going to work either. ;)
Saving the game and loading later, changing characters, or leaving the lot etc... would reset it.
