Elevated natural killer cell levels and autoimmunity synergistically decrease uterine blood flow during early pregnancy

OBJECTIVE To investigate whether natural killer (NK) cell and autoimmune antibody acts synergistically, by the action of autoantibodies to increase NK cell number and cytotoxicity, to decrease uterine blood flow during early pregnancy in pregnant women with a history of recurrent spontaneous abortion (RSA). METHODS Seventy-five pregnant women (between 5 and 7 weeks gestation) with a history of unexplained RSA were included in the study group. Forty-one pregnant women without a history of RSA were included as controls. All women with a history of RSA were tested for autoantibodies and number of peripheral blood natural killer (pbNK) cell by flow cytometry. Study populations were stratified into four groups by existence of autoantibody and degree of increase of pbNK cells. The uterine radial artery resistance index (RI) was measured by color-pulsed Doppler transvaginal ultrasound. RESULTS The mean RI of the autoimmune antibody-positive (AA+) group (0.63±0.09) was significantly higher than that of the normal control group (0.53±0.10, P=0.001). The mean RI of the AA+/only-NK elevated (eNK) group (0.63±0.09) was significantly higher than those of the only-AA+ group (0.55±0.07, P=0.019) and the only-eNK group (0.57±0.07, P=0.021). CONCLUSION Concurrent elevation in NK cells and autoimmunity results in decreased uterine blood flow during early pregnancy. However, the majority of cases of RSA remain unexplained and larger scale studies are needed to confirm our conclusion and to develop diagnostic and therapeutic plans for women with a history of RSA.