Threatened miscarriage refers to the symptoms indicating an impending miscarriage, often characterized by significant lower abdominal pain and vaginal bleeding. During a threatened miscarriage, intense activities should be avoided, appropriate rest is necessary, and sexual intercourse should also be avoided. Engaging in sexual intercourse during a threatened miscarriage can cause the following harms: First, intercourse can stimulate the uterus, causing lower abdominal pain, which can lead to uterine contractions. These contractions can stimulate the gestational sac, and in severe cases, can trigger a spontaneous miscarriage. Second, sexual activity can stimulate the vagina and alter the vaginal flora, which sometimes can lead to vaginitis. Vaginitis can spread through the cervix into the uterine cavity, sometimes causing endometritis, affecting the development of the gestational sac and in severe cases can also lead to a spontaneous miscarriage. Therefore, it is crucial not to engage in sexual intercourse when symptoms of a threatened miscarriage appear.