Recurrent pregnancy loss (RPL) affects 1-3% of women. An emerging likely aetiology in unexplained RPL is failure of maternal immune tolerance. Maternal T regulatory (Treg) cells are critical for orchestrating this active immune tolerance and ensuring optimal embryo implantation. This study aims to provide a comprehensive analysis of the T cell subsets in women with RPL. Peripheral blood was collected at the mid-luteal phase of the cycle in women with RPL (n=27) and proven fertile controls (n=15). T cell phenotypes were analysed by multi-coloured flow cytometry. Conventional gating strategies were utilised to demonstrate that within the CD4+ T cell compartment, there was a 34% decline in the proportion of FOXP3+ Treg cells in RPL patients. Despite women with RPL having fewer Treg cells, they were more activated, with fewer naïve and more central memory Treg cells, compared to fertile controls, as assessed by CCR7 and CD45RA expression. Supporting this, Treg cells within the RPL women were more proliferative, as measured by Ki67 expression, and had a higher proportion of the highly suppressive HLADRhiCD45RA- Treg cell phenotype, although they had reduced expression of CTLA4. Analysis of the proportion of CD4+ Tconv cells expressing the Th1 and Th17 transcription factors Tbet and RORgt respectively, showed a trend towards more Th1 cells and a significant rise in Th17 cells in RPL women, leading to a dramatic decrease in both the Treg:Th1 and Treg:Th17 ratio, compared to women of proven fertility. Taken together these data show a decline in Treg cell abundance in women with RPL, although this population of Treg cells has a phenotype shifted towards greater proliferation, activation and suppression. Future studies will examine the functional consequences of these phenotypic changes.