A few weeks into pregnancy, amniotic fluid.

Under normal circumstances, amniotic fluid begins to appear at more than eight weeks of pregnancy. At the beginning, the amount of amniotic fluid will be relatively small. After the placenta is formed, the amount of amniotic fluid gradually increases. In the second trimester of pregnancy, the amniotic fluid mainly comes from the urine of the fetus. In the third trimester of pregnancy, in addition to the urine of the fetus, there are amniotic fluid produced by fetal membranes and umbilical cords. The amount of amniotic fluid in the second trimester of pregnancy will be relatively more, and in the third trimester of pregnancy, the amount of amniotic fluid may gradually decrease due to the decline of placental function. Therefore, color Doppler ultrasound examination should be carried out regularly in the third trimester of pregnancy to understand the condition of amniotic fluid, so as to prevent intrauterine hypoxia caused by oligohydramnios, and even fetal death in severe cases.