NK cell activity and estrogen hormone levels during normal human pregnancy.

NK cell activity was determined in peripheral blood of 24 women during pregnancy, and compared to NK activity of 40 healthy nonpregnant women in generative age. An increase in the first trimester was followed by a significant decline of NK activity in the second trimester, and a further fall in the third trimester of pregnancy. The initial rise of NK activity was predominantly due to primigravidas, whereas the fall in the second trimester was mainly due to multigravidas. There was a significant negative correlation between NK activity and the increasing levels of estrogen hormones (beta-estradiol, estriol and estrone) in the sera of pregnant women. However, when analyzed for each trimester of pregnancy separately, a significant (p less than 0.02) negative correlation was only found with beta-estradiol, suggesting that high doses of this hormone could contribute to pregnancy-associated NK suppression.