Forty days pregnant with low progesterone should follow the doctor’s instructions medication to preserve the fetus treatment, and review on time. The normal value of progesterone at forty days of pregnancy can be 20~25ng/ml, when the progesterone test is low and the ultrasound suggests intrauterine pregnancy, there may be the risk of preeclampsia, considering the luteal insufficiency, need to rest, prohibit sexual intercourse, and follow the doctor’s instructions to give progesterone injection intramuscular injection or oral progesterone progesterone and other progesterone preparations to preserve the fetus treatment. After treatment, progesterone should be rechecked again, when the result of progesterone is normal, and ultrasound suggests that the embryo is well developed, the pregnancy can continue. However, if the value of progesterone is still low, it is necessary to continue drug treatment, and then review the test after 7 to 10 days. If the symptoms still do not improve, or continue to decline, and the ultrasound suggests that the embryo is underdeveloped, it is necessary to terminate the pregnancy.