Asthma is a common chronic disease that may complicate pregnancy and a risk factor for complications; however, immunological mechanisms of the bilateral interactions between asthma and pregnancy are not fully understood. Healthy gestation is characterized by a sensitive balance of T(h)1/T(h)2/T(h)17/regulatory T (Treg) cells that may be altered in asthmatic pregnancy. The aim of this study was to describe the prevalence of these cell subsets in asthmatic compared with healthy pregnancy. The prevalence of T(h)1, T(h)2, T(h)17 and Treg lymphocytes was identified by cell surface and intracellular marker staining in blood samples of 24 healthy non-pregnant (HNP), 23 healthy pregnant (HP), 15 asthmatic non-pregnant (ANP) and 15 asthmatic pregnant (AP) women using flow cytometry. The T(h)1/T(h)2 cell ratio was decreased in both HP and ANP compared with HNP women; however, no further decrease was observed in the AP group. The T(h)17/Treg ratio was decreased in HP, but not in AP women, compared with HNP data. Healthy pregnancy increased Treg cell prevalence compared with HNP data (4.64% versus 2.98%; P < 0.05), and this pregnancy-induced elevation was absent in AP women (2.52% versus 4.64%; P < 0.05). T(h)17 cell prevalence was similar in the HP and HNP groups (2.78% versus 3.17%; P > 0.05). Asthma increased T(h)17 prevalence in non-pregnant patients (3.81% versus 3.17%; P < 0.05), and this asthma-specific increase of T(h)17 cell prevalence was also observed in AP patients (AP versus HP: 3.44% versus 2.78%; P < 0.05). The abnormal asthma-dependent T(h)17 elevation together with blunted Treg increase may play a role in the compromised immune tolerance characterizing asthmatic pregnancy.