Vaginal Progesterone to Prevent Preterm Delivery in Women With Preterm Labor

Inclusion Criteria: * Gestational age between 240/7 et 336/7 weeks of gestation (based on a reliable estimate by ultrasound performed before 22 weeks) * Singleton pregnancy * Intact membranes * Preterm labor defined as: * 2 or more regular and painful uterine contractions in 10 minutes plus one or plus of the following criteria: * short cervix detected by vaginal ultrasound scanning (cervical length less than 30 mm until 31 weeks and less than 25 mm from 32 weeks) * cervical changes detected clinically (cervical length less or equal 10 mm or Bishop score less than 6 * cervical changes during hospitalization (more or equal 5 mm between two clinical or US exams) * positive fetal fibronectin * Age ≥ 18 years old * Signed informed consent * Possible and accepted follow-up Exclusion Criteria: * Multiple gestation * Cervical cerclage * Hydramnios (AFI \>95th percentile for gestational age or greatest pocket \>8 cm) * Premature rupture of membranes * Chorioamnionitis (criteria for clinical diagnosis are: elevated WBC, elevated CRP, maternal tachycardia, fetal tachycardia, uterine tenderness and/or amniotic fluid foul odor) * Cervical dilatation \> 3 cm * Placenta praevia or abruptio placentae * Intra-uterine growth restriction or non-reassuring fetal status * Pre-eclampsia or severe hypertension * Any other maternal or fetal pathology which should indicate medically preterm delivery