The causes of high neutrophils are the following: first, the endocrine system is hyperfunctional, the cell proliferation and division are precisely regulated by the endocrine system, especially the influence of hormones, the endocrine system is enhanced when pregnant, neutrophils are high. Second, the body is in a state of stress when pregnant, the body for self-protection, the immune system is hyperfunctional, so that neutrophil division and proliferation is accelerated, neutrophils are high. Thirdly, the circulating blood volume of the mother’s body is redistributed during pregnancy, and the circulating blood volume tends to flow to the fetus, and the circulating blood volume of the mother’s body is reduced compared to that before pregnancy, resulting in high neutrophils. Fourth, the number of other blood cells decreases, such as lymphocytes, eosinophils, and monocytes, causing high neutrophils.