Asthma is one of the most common chronic inflammatory lung diseases among pregnant women. Acute asthma exacerbations during pregnancy negatively impact pregnancy outcomes. As myeloid-derived suppressor cell (MDSC) populations are known regulators of airway inflammation and are important in maternal-fetal tolerance, we investigated if percentages of circulating MDSC subsets correlated with clinical indicators of airway inflammation and maternal-fetal tolerance in a cohort of healthy pregnant (HP), asthmatic pregnant (AP) and well controlled asthmatic pregnant (WCAP) women recruited to the B-WELL Mom study. Reciprocal dynamics of circulating MDSC subsets, with granulocytic MDSCs (Gr-MDSCs) increasing over early pregnancy and declining in late stage pregnancy and the reverse trend with monocytic MDSCs (Mo-MDSCs) were identified; the decline of Mo-MDSCs at Visit 3 of pregnancy was higher in AP/WCAP compared to HP whereas the decline of Gr-MDSCs at late stage pregnancy was lower in AP/WCAP compared to HP. In AP/WCAP, positive correlations were observed between both MDSC subsets during pregnancy and Gr-MDSCs correlated positively with fractional exhaled nitric oxide, a surrogate measure of airway inflammation, during early pregnancy; these relations were not identified in HP subjects. Interestingly, soluble HLA-G as well as indoleamine 2,3 dioxygenase activity, both important in maternal-fetal tolerance, showed positive correlations with MDSCs only in HP and not in AP/WCAP subjects. Our studies suggest that differential myeloid-cell dynamics may serve as biomarkers of maternal-fetal tolerance in AP/WCAP subjects.