Prediction of spontaneous preterm birth: salivary progesterone assay and transvaginal cervical length assessment after 24 weeks of gestation, another critical window of opportunity.

Measurement of salivary progesterone (SP4) levels and cervical length (CL) after 24 weeks to assess their potential predictive value among asymptomatic women at high risk of spontaneous preterm birth (PTB). This prospective observational (noninterventional) study consecutively recruited asymptomatic women at high risk of spontaneous PTB. SP4 and CL were measured at recruitment (24-28 weeks of gestation) then repeated after 3-4 weeks.