There are three main reasons for low urea in pregnancy: First, the kidney volume increases, and the glomerular filtration rate increases. Women’s kidney volume will increase during pregnancy, and the ability to remove toxins will increase, called the glomerular filtration rate increases. And urea, like creatinine, is also a kind of toxin, so a large amount of urea is excreted out of the body, resulting in low urea concentration. Second, the body fluid dilution, women’s body during pregnancy will increase the fluid, for any substances have a dilution effect, such as for hemoglobin dilution will cause mild anemia, and for urea dilution will lead to low urea concentration. Third, early pregnancy reaction, women in the early stages of pregnancy early reaction is more serious, no appetite for anything, but also nausea, vomiting, of course, the intake of protein will also be reduced. Urea is the metabolite of protein, so from this aspect will also lead to low urea concentration.