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

OBJECTIVE

To assess whether cervical size in the early second trimester and cervical ripening at term may be related to serum levels of endogenous relaxin, 17beta-oestradiol or progesterone.

DESIGN

A cross-sectional study investigating the relationship between hormone concentrations and cervical parameters as measured by ultrasound and Bishop score, respectively.

PARTICIPANTS

Uncomplicated human pregnancies with normal fetal outcome, 72 women in the second trimester and 40 women at term.

METHODS

Vaginal ultrasound and palpation were used to estimate cervical parameters. Hormones were analysed either by dissociation-enhanced fluoroimmunoassay (relaxin) or by automated electrochemiluminescent immunoassays.

RESULTS

Cervical length and diameter correlated positively during mid-gestation and negatively at term. During mid-gestation, but not at term, relaxin was significantly associated with cervical length and volume, and with progesterone. Bishop score only correlated inversely with progesterone at term.

CONCLUSION

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.