This is a bit of a sensitive subject, but it's something that new parents should know before the big day comes and baby boy arrives. It's not out of the norm, your tiny newborn baby boys testicles are... ummm...to put it delicately...huge! Before your hubby takes credit for juniors' special gift he should know that this is true of ALL newborn baby boys. Swelling of the testicles is actually caused in part by the pressure that is exerted on your baby during birth and fluids that get trapped in the tissue. Also, all new babies still have Mom's hormones circulating in their body. For boys, these hormones mean enlarged testicles and for girls, they cause the labia to swell. Your hubby will stop patting himself on the back after a couple of days as swelling subsides.