Inclusion Criteria:  Pregnant women with singleton pregnancies admitted with a diagnosis of preterm labor between 23.0 and 34.6 weeks, not in labor at randomization and who do not meet exclusion criteria.  Exclusion Criteria:  Women who do no accept to be part of the study Maternal age < 18 years Multiple gestations Clinical chorioamnionitis at randomization (defined by the presence of fever above 38 celsius degrees (ºC), fetal tachycardia (>160 heart beat per minute >10 minutes), maternal White blood cells > 15000/mm3 (not justified by the administration of antenatal steroids). Cervical dilatation > 3 cm Major structural malformations of fetal complications that are related to neurodevelopmental impairment. Technical problems to perform an amniocentesis (prediction models include information from amniotic fluid: glucose and IL-6 concentration).