Relaxin used to produce the cervical ripening of labor.

Important progress has been made in understanding the physiology of relaxin in human pregnancy. The structure of relaxin and its genetics have been elucidated. Progress has been made into understanding the control of relaxin secretion. Many actions of relaxin have been defined. Some of the effects of too much or too little relaxin have been described. However, the cellular mechanisms of relaxin action must still be determined, and the relationship of relaxin to diseases of pregnancy must be clarified. Although relaxin affects the human cervix, its physiologic role is not clear. Pregnancies can proceed uneventfully in the absence of circulating relaxin. Thus circulating relaxin is not critical for maintaining pregnancy or for cervical ripening. The mechanisms by which pregnancy is maintained and the mechanism of the timely onset of labor at full term are not well understood. There is a plethora of data suggesting many parallel overlapping control mechanisms for uterine control. Most of these systems are not critical because their actions can be compensated for by other systems. Understanding the physiology of human pregnancy must account for these multiple systems. Within this context, the role of relaxin in the physiology of labor must be understood.