The role of the hormone relaxin in human reproduction and pelvic girdle relaxation.

Relaxin is a polypeptide hormone produced in the human female by the corpus luteum of pregnancy and the decidua. In the male it is produced in the prostate and is present in human semen. It probably plays a paracrine role in the human and thus peripheral serum levels may not always reflect its activity. Although a large amount of pelvic relaxation is necessary in some species, such as rodents, for successful parturition, little increased joint mobility is necessary at human parturition. However, some women experience much greater degrees of pelvic girdle relaxation on average and this appears to be more common in the Scandinavian countries than the rest of the world. Studies are presented showing an association between high serum relaxin levels and symptom giving pelvic girdle relaxation during pregnancy. It is not yet possible to measure relaxin receptors in these women but high levels of relaxin or a susceptibility to relaxin may be contributing to this problem. Before considering manipulating relaxin levels or down grading relaxin receptors to try to improve the symptoms of pelvic girdle relaxation it is important to understand the many other roles of relaxin in the human. Evidence is presented that suggests that relaxin may have significant roles in sperm motility, fertilisation, implantation, uterine growth and accommodation, the control of myometrial activity to prevent preterm labour, cervical ripening and the facilitation of labour. The management of pelvic girdle relaxation is discussed.