Relationship of serum levels of endogenous relaxin to cervical size in the second trimester and to cervical ripening at term.

Corpus luteum function is reflected by progesterone and relaxin in the early second trimester. An impact of relaxin on cervical growth, previously demonstrated by animal models and in vitro experiments, was confirmed during human mid-gestation. In contrast to many other species, human cervical ripening was not associated with endogenous relaxin at term, but with decreased progesterone.