Recurrent miscarriage (RM), defined as two or more pregnancy losses before gestational week 24, affects ~5% of women. The underlying causes are not known, although emerging evidence suggests immune dysregulation is a common cause of idiopathic RM. Immune cells and factors are key determinants of endometrial receptivity and capacity to establish healthy pregnancy, particularly CD4+ regulatory T (Treg) cells which control inflammation and assist in vascular remodelling. Suboptimal Treg cell responses are irrefutably shown to cause pregnancy loss in animal models and in women, are associated with infertility and a range of pregnancy complications. Here we aimed to elucidate phenotypically distinct peripheral blood T cell populations between RM patients and healthy control women by assessing multi-coloured flow cytometry data using the machine learning, dimensionality reducing algorithm t-distributed stochastic neighbour embedding (t-SNE). Peripheral blood samples were collected from n=27 RM patients and n=15 control women with no history of RM at the mid-luteal phase of the menstrual cycle. CD3, CD4 and CD8 lineages were assessed using 18 colour flow cytometry panels. Only CD4 T cells showed significant changes between groups. To dissect the specific CD4+ T cell changes in RM Th1, Th2, Th17 and Treg cell abundance and phenotype was evaluated. The mean proportion of CD25+FOXP3+ Treg cells within the CD4+ T cell compartment was reduced by 44% in RM compared to control women (P<0.01). Additionally, fewer terminally differentiated effector memory Treg cells and a subset of highly suppressive and proliferative Treg cells was identified in RM patients, with greater expression of Ki67, HLD-DR and CTLA4. This data suggests that women experiencing idiopathic RM have reduced Treg cells and specifically, exhibit a memory Treg cell deficiency consistent with premature Treg cell exhaustion. This analysis gives new insight on the nature and underlying causes of immune dysfunction in some RM women.