Pain in early labor is limited to dermatomes :
In the early stages of labour pain is mainly uterine in origin because of painful uterine contraction
“The pain of uterine contractions is distributed along the cutaneous nerve distribution of T10 to L1"
In later stages pain is due to dilatation of the cervix.
“The pain of cervical dilatation and stretching is referred to the back through sacral plexus.”
T10 − L1
S1 − S3
L4 − L5
L2 − L3