Thirty-one weeks of pregnancy has entered the late stages of pregnancy, during which time intercourse is not allowed, until delivery. Because the condition of the cervix starts to mature after 28 weeks, and the uterus is very sensitive, after the stimulation of sexual life, it is easy to induce uterine contractions, resulting in preterm labor. In the process of sexual intercourse, if the amplitude is too large, it may also lead to premature rupture of the fetal membranes, or cause vaginitis and infection, etc. These conditions are very unfavorable to the pregnant woman and the fetus. The woman must pay attention to controlling her sex life during pregnancy, even more so in the late pregnancy. If a fetus is born prematurely at 31 weeks, the survival rate after birth is still not very high.