Which nerve injury results in decreased sensation of the labia after a cesarean delivery?

Decreased sensation of the labia after a cesarean delivery is primarily attributed to injury of the ilioinguinal nerve. This nerve is responsible for providing sensory innervation to the skin over the lower abdomen, as well as to the labial and inner thigh areas. During a cesarean delivery, the ilioinguinal nerve can be susceptible to damage due to the incision made in the lower abdominal wall or due to retraction during the surgery, which may lead to numbness or altered sensation in the associated areas.

The iliohypogastric nerve also provides some sensation to the lower abdomen but is less involved in the sensory supply to the labia. The obturator nerve and femoral nerve primarily supply the inner thigh and anterior thigh regions, respectively, and are not directly related to sensation in the labial area. Hence, the ilioinguinal nerve's direct role in innervating the labia makes it the most relevant choice for this context.