MATERIAL AND METHODS: 200 patients with a singleton pregnancy between 24 and 34 weeks of amenorrhea and complicated PTL, will be prospectively included in the maternity wards of Galway (Ireland) and of Dijon with the support of the perinatal network of Burgundy. A 2X5ml blood sample will be collected upon admission, at D1, D2, D4 and D6 for women who did not deliver within the first 7 days; finally, another blood sample will be drawn upon discharge. After delivery, foetal membranes will be collected to characterize and compare the various monocyte and lymphocyte subpopulations in the maternal blood. The characterization and the study of the level of activation of blood and foetal membrane cells will be performed using flow cytometry technique with suitable markers. The main judgment criteria will be the percentage of monocytes positively expressing MCP-1 for all three monocyte subpopulations ("inflammatory", "residents or patrollers" and "intermediates", according to CD14, CD16, CCR2 and MCP-1 markers. Lymphocyte subpopulations will be assessed using the following markers: CD45, CD3, CD4, CD8 (T lymphocytes), HLA-DR (activated T lymphocytes), CD19 (B lymphocytes), CD16/CD56 (NK Cells), intracellular IFN-gamma (Th1 lymphocytes), intracellular IL-4 (Th-2 lymphocytes), intracellular IL-17 and CCR6 (Th17 lymphocytes), CD4, CD25, Foxp3 and CD127 (Tregs). Univariate statistical analysis of quantitative data will be performed using the Mann and Witney test or ANOVA, after verification of the conditions of application. The comparisons of percentages will be done using Chi-square Pearson tests and the Fisher's exact test, as appropriate. The multivariate analysis will be performed using a stepwise descending analysis.