As you have learned, cats do NOT approve of any tampering with their bathroom facilities! This includes:
- moving the box
- changing the box (buying a new one)
- changing the brand of litter
- changing anything immediately around the box.

See if the problem continues now that you have replaced the box.

Oh, and you should have the cat neutered before baby arrives. Male cats may mark their territory, and once baby is around, there will be lots of urine and other new smells around. Neutering is not a sure way to prevent marking -- he may do it anyway. But there is less chance, if he is neutered.