Abstract Background Threatened preterm delivery (TPD) is the leading cause of inpatient admissions during pregnancy. The ability to predict the risk of imminent preterm delivery is thus a major priority in obstetrics. The aim of our study is to assess the diagnostic performance of the test to detect the placental alpha microglobulin 1 (PAMG-1) for the prediction of delivery within 7 days in women with TPD. Methods This is a prospective multicenter diagnostic study. Inclusion criteria are singleton pregnancy, gestational age between 24 + 0 and 33 + 6 weeks inclusive, cervical measurement 25 mm or less assessed by transvaginal ultrasound (with or without uterine contractions), clinically intact membranes and cervical dilatation < 3 cm assessed by digital examination. According to the current protocol, when a women presents with TPD and the diagnosis is confirmed by transvaginal ultrasound, a vaginal sample to test for genital infection is performed. At the same time, the midwife will perform the PartoSure® test. To perform this analysis, a sample of cervicovaginal secretions is taken with the vaginal swab furnished in the test kit. The primary outcome is the specificity of the PartoSure® test of women who gave birth more than 7 days after their hospitalization for TPD. The secondary outcomes are the sensitivity, PPV, and NPV of the Partosure® test and the factors associated with false positives (with a univariate logistic regression model). Starting with the hypothesis of an anticipated specificity of 89%, if we want to estimate this specificity with a confidence interval of ± 5%, we will require 151 women who do not give birth within 7 days. We therefore decided to include 400 women over a period of two years to have a larger number of events (deliveries within 7 days). Discussion The different tests already used such as fetal fibronectin and phIGFBP-1, are not sufficiently relevant to recommend their use in daily practice. The different studies of PAMG-1 described above thus provide support for the use of this substance, tested by PartoSure®. Nonetheless, other larger studies are necessary to validate its use in daily practice and our study could answer this question. Trial registration NCT03401255 (January 15, 2018)