Low urea nitrogen in pregnant women is often caused by physiological factors, for example: First, after pregnancy, the blood volume in the body will increase significantly, which leads to an increase in the blood flow of the kidneys, glomerular filtration rate increases, so the urea nitrogen eliminated from the body will increase, resulting in a decrease in the body’s urea nitrogen. Second, because of the increase in blood volume of pregnant women, resulting in dilution, so the measurement of urea nitrogen will also appear low results. Third, some pregnant women during pregnancy, there will be obvious nausea, vomiting, eating less, may be due to insufficient protein intake, resulting in low urea nitrogen. In addition to physiological factors, it is also necessary to pay attention to whether there are any pathological factors. For example, the patient himself has a combination of liver disease, resulting in reduced protein synthesis caused by low urea nitrogen, or there are no renal problems resulting in low urea nitrogen, to actively review the relevant indicators.