Based on the description provided, the baby's diagnosis is likely to be spina bifida. Spina bifida is a birth defect in which the neural tube, which develops into the spinal cord and meninges, does not close properly during fetal development. This can result in a protrusion of the spinal cord and meninges through an opening in the spine, typically in the lower back. Spina bifida can range in severity from mild to severe and may require medical intervention and management depending on the specific case.