Knee pain in late pregnancy may be caused by physiological factors, synovitis, calcium deficiency and other factors. 1. Physiological factors: in late pregnancy is due to the fetus is larger, and pregnant women weight increase significantly, will make the knee joints under increased pressure, long time standing or activities, it is easy to cause knee pain, reasonable rest can be improved on their own. 2. synovitis: in late pregnancy, due to the knee joints under pressure, and in daily exercise time is too long, do not pay attention to the knee joint parts of the warmth, can lead to synovial membrane damage, caused by synovitis, will cause the symptoms of knee pain, standing time is too long, the symptoms of pain will be significantly aggravated, and when accompanied by serious joint swelling. 3. Calcium deficiency: in late pregnancy, the body lacks calcium more, can also cause knee pain, may also often appear leg cramps. If the knee pain in late pregnancy lasts for a long time, it is recommended to consult a doctor for examination to clarify the specific cause and carry out appropriate treatment under the guidance of the doctor.