When a placenta previa occurs, it is likely to lead to premature birth. Placenta previa is a condition where, after 28 weeks of pregnancy, the placenta is positioned low in the uterus, often below the presenting part of the fetus, and attaches to the lower segment of the uterus or near the internal os of the cervix. In the late stages of pregnancy, dilation of the cervix can cause the placenta to be misaligned with the uterine wall, leading to recurrent, painless bleeding. When the bleeding reaches a certain amount, it can easily lead to premature separation of the placenta, inducing uterine contractions and the onset of premature birth. In cases of placenta previa with significant vaginal bleeding, it is necessary to terminate the pregnancy promptly.