Generally speaking, there is no need to take progesterone supplements after the third trimester of pregnancy, but there are some special cases in which progesterone should be used to protect the fetus. Before the third trimester of pregnancy progesterone is secreted by the ovaries, etc. After the third trimester progesterone is mainly secreted by the placenta, which secretes a relatively large amount to meet the needs of the pregnant woman and the fetus, and this time period is also a relatively stable period, with relatively fewer chances of preeclampsia or miscarriage. However, some women who have recurrent miscarriages or have irregular contractions or small amounts of vaginal bleeding due to mechanical stimuli such as strenuous exercise or trauma can also apply progesterone to preserve the fetus, because progesterone can relax the smooth muscle and inhibit uterine contractions to achieve the purpose of preserving the fetus.