5β-Dihydroprogesterone and Human Preterm Labor

We previously investigated the progesterone metabolite 5β-dihydroprogesterone (5βDHP) in relation to human parturition at term, demonstrating that peripheral venous concentrations decrease in association with the onset of spontaneous labour. In this study our aim was to determine if 5βDHP concentrations were lower in women presenting in spontaneous preterm labour than in controls matched for gestational age. Blood samples were obtained from women presenting in spontaneous preterm labour (n = 20). The diagnosis was made on the presence of regular contractions and cervical effacement and dilatation of at least 3 cms. All women in the preterm labour group delivered before 37 weeks gestation. Blood samples were then obtained from controls, closely matched for gestational age with uncomplicated pregnancies. The preterm labour group was further stratified by cause into three groups, chorioamnionitis (n = 5), abruption (n = 4) and idiopathic (n = 11). Following organic solvent extraction, steroids were separated by HPLC and 5βDHP quantified by radioimmunoassay. Women in the idiopathic preterm labour group were found to have significantly lower circulating concentrations of 5βDHP than controls (p < 0.05). There were no significant differences found in either the chorioamnionitis or abruption groups. This result suggests that there may be a group of women in whom the normal endocrine process of labour is triggered early resulting in preterm labour.