Cervical insufficiency is often presented as painless dilation of the cervix，while the clinical manifestations of cervical insufficiency in the first pregnancy are more insidious. Cervical ultrasound detection for high-risk pregnant women can identify suspected cervical insufficiency at an early stage. There is no consensus among countries on the need for ultrasound cervical length screening for all women in their second trimester，but it is certain that the most important significance of universal screening is to detect high-risk women who are preterm in their first pregnancy and to prevent late abortion and preterm birth. Women with a history of second-trimester miscarriage or preterm birth but no reasonable indication of cervical cervix shortening（CL≤25mm）may benefit from cervical cerclage. In addition，the most important thing to target the cause of short cervix is to rule out the cervical changes caused by infectious factors. The significance of ultrasonic cervical examination after cervical cerclage lies in the individual decision-making according to the specific condition.