Changes in uterine innervation in pregnancy and during labour

Abstract

The present review highlights recent findings focusing on effects on the cervical innervation exerted by term pregnancy and labour. The corpus uteri is almost denervated in term pregnancy, as demonstrated in both humans and rodents, whereas the cervical innervation remains dense throughout pregnancy and labour. In rats, fewer connections between sensory subdivisions in spinal cord segments and the cervix have been observed in late pregnancy as compared with the nonpregnant state. In term pregnancy an increased excitability of mechanosensitive afferents innervating the cervix has been demonstrated. The reasons for these seemingly contradictory findings may be clarified in further studies. Transient receptor potential vanilloid receptor, a key molecule in nociception, has been identified in the human cervix uteri in the nonpregnant state and during pregnancy and labour as opposed to the corpus, in which transient receptor potential vanilloid receptor disappears during pregnancy. These findings add evidence to the hypothesis that the uterine cervix is the main site from where labour pain propagates. The conservation of the cervical innervation in term pregnancy and labour, in contrast to the corpus, and the large number of mediators involved in cervical ripening clearly indicate that the cervix plays a crucial role in pregnancy maintenance, labour initiation, labour pain and parturition.