1. What is cervical insufficiency? Cervical insufficiency is often used to describe those who have a spontaneous miscarriage in mid-pregnancy, where the cervix is considered too “weak” to maintain a closed cervix and thus insufficient to maintain the pregnancy, resulting in a miscarriage. The clinical characteristic is painless cervical dilatation or protrusion of the amniotic sac (“amniotic protrusion”) in mid-pregnancy, i.e., miscarriage following contractions, vaginal bleeding, infection, or uterine hypertonicity, which in theory should not be diagnosed as cervical insufficiency. Previously, the diagnosis of cervical insufficiency was only considered in cases of recurrent midtrimester miscarriage, but in 2014 the American College of Obstetricians and Gynecologists (ACOG) recommended that the diagnosis be made with just one of these classic symptoms. 2. How is cervical insufficiency determined? In fact, cervical insufficiency is a less accurate clinical diagnosis, describing a state of “incompetence” of the cervix. Therefore, as of today, there is no unified and definitive method to confirm the diagnosis. The most commonly used clinical tests include manual examination, hysteroscopy, ultrasound to measure the length of the cervix, hysteroscopy, and hysterosalpingography, all of which are unable to make a definitive diagnosis. The most commonly used ultrasound for monitoring cervical length changes in mid-pregnancy is the 10th and 90th percentile of normal cervical lengths of 25 mm and 45 mm, respectively, and we often use a cut-off of less than or equal to 25 mm to diagnose a shortened cervix. If the cervix is short, there is an increased risk of preterm delivery, but a short cervix alone cannot diagnose the presence of cervical insufficiency. 3. What are the causes of cervical insufficiency? There are congenital and acquired causes of cervical insufficiency, the latter being mainly surgical and childbirth injuries to the cervix, including cervical conization, cervical LEEP, repeated mechanical dilatation of the cervix (hysteroscopy, abortion) or cervical tears caused by childbirth. Of course, not all the literature agrees; for example, there is no unanimous opinion on whether trauma to the cervix caused by multiple hysteroscopies and abortions can cause cervical insufficiency. As to whether cervical “function” is affected by the damage caused by cervical conization or LEEP, it also depends on the amount of tissue removed and the length of the cervix after the procedure. This is relatively easy to understand. If more cervical tissue is removed, then there is less connective tissue and fibers to maintain the “function” of the cervix, which may result in incompetence. Congenital factors include hypoplastic Mullerian ducts, cervical collagen and elastin deficiency, or intrauterine ethylene estradiol exposure, but these are relatively uncommon.