Pregnancy presents the maternal immune system with a unique immunological challenge since it has to defend against pathogens while tolerating paternal allo-antigens expressed by fetal tissues. T helper (Th) cells play a central role in modulating immune responses and recent advances have defined distinct contributions of various Th cell subsets throughout each phase of human pregnancy, while dysregulation in Th responses show association with multiple obstetrical complications. In addition to localized decidual mechanisms, modulation of Th cell immunity during gestation is mediated largely by oscillations in sex hormone concentrations. Aberrant Th cell responses also underlie several autoimmune disorders while pregnancy-induced changes in the balance of Th cell immunity has been shown to exert favorable outcomes in the progression Th1 and Th17 driven autoimmune conditions only to be followed by post-partal exacerbations in disease. •Dynamic adaptations in T helper cell immunity are vital for successful pregnancy•Aberrant T helper cell responses are associated with adverse pregnancy outcomes•Sex hormone fluctuations exert profound systemic changes in maternal T helper cell immunity during pregnancy•Pregnancy can induce spontaneous remission followed by post-partal disease flares in Th1 and Th17 driven autoimmune disorders