[Clinical analysis of the pain pathways of labor (author's transl)].

Segmental epidural blocks by double catheters which were inserted in the thoracolumbar (Th12-L1) and lower lumbar region (L4-L5) were performed in eleven primiparas to investigate the correct pain pathways of labor and the sensory innervation of uterus. It is generally believed in Japan that the sensory nerves of the cervix of uterus enter the cord through the sacral segments (s2,3,4) and the uterine body through the thoracic segments (Th11, Th12). 5 ml dose of 0.5% bupivacaine (Marcaine) was used to the upper catheter (Th12-L1) during the first stage of labor. Segmental spread of analgesia was on average Th9.4-L1,6 and the duration was 1 hr 57 min +/- 34 min. Seven cases (64%) had no pain up to the full dilatation of cervix and four cases (36%) complained of the pain in the pudendal nerve region (S2,3,4) at the 8 cm dilatation of cervix due to the lower engagement of the fetal head. These findings suggest that not only the pain impulses during the first stage of labor which are resulted from the uterine contraction and the dilatation of the cervix enter the cord through Th10.Th11.Th12.L1 segments and no relation to sacral nerves.