Bacteriuria during pregnancy is one of the most common diseases in women during pregnancy, with an incidence of 4% to 10%. The most common pathogenic bacteria in bacteriuria during pregnancy are Escherichia coli, accounting for about 80% or more, followed by S. pyogenes, Klebsiella, S. aerogenes, Enterococcus, Streptococcus faecalis, and Staphylococcus aureus or Staphylococcus albus. These bacteria are already present in the urethra before pregnancy. In early pregnancy, due to the increased secretion of progesterone, the tension of the renal pelvis, renal calyces and ureter is reduced, and in late pregnancy, the enlarged uterus compresses the ureter (especially the right ureter), which can make the urine excretion poor and stagnant, all of which are conducive to the reproduction of bacteria. In addition, the increase in nutrients in the urine of pregnant women is also conducive to the growth of bacteria. Pressure and injury to the bladder during delivery, difficulty in urination after cesarean delivery and the use of catheters also increase the chances of bacterial episodic infection. As a result, the risk of bacteriuria is greatly increased during pregnancy. It has been found that the older a pregnant woman is and the more pregnancies she has, the greater the risk of bacteriuria. Reasons why bacteriuria is likely to occur during pregnancy: 1. Progesterone effect: During pregnancy, under the effect of high progesterone, the ureteral wall relaxes, the wall dilates and peristalsis decreases. Weak contraction of intestinal smooth muscle, prone to constipation, colonic hepatic flexure adjacent to the right kidney, intestinal bacteria invade the right kidney along the lymphatic vessels. 2. Pregnant uterus compression: the enlarged pregnant uterus compresses the ureter at the entrance of the pelvis, blocking the flow of urine. Pregnant uterus mostly rotates to the right, and the right ureter is more likely to be compressed. The left ureter is lined with sigmoid colon in front of the ureter, which acts as a buffer, so the incidence of infection on the right side is more than that on the left side. 3, other: in the middle and late stages of pregnancy, pelvic stasis, the uterus and fetal head push pressure on the bladder, easy to make urination.