Final answer:
The priority nursing diagnosis for a baby preoperative for closure of a myelomeningocele is Risk for Infection, due to exposed tissues and nerves that increase susceptibility to infection.
Step-by-step explanation:
The baby's priority nursing diagnosis preoperative for closure of a myelomeningocele is Risk for Infection. Myelomeningocele is a severe form of spina bifida where the meninges protrude through an opening in the spine, potentially exposing tissues and nerves, thereby increasing the risk for infection. This is a concern due to the vulnerability of the exposed tissues and the risk of potential complications from surgical interventions. The focus is on preventing infection prior to surgery to ensure the best possible outcome and to minimize further damage or complications that can arise from infections at the surgical site.