Cervical insufficiency is the inability of the cervix to retain fetus, in the absence of uterine contractions or labor (painless cervical dilatation), owing to a functional or structural defect. It is cervical ripening that occurs far from the term. Cervical insufficiency is rarely a distinct and well defined clinical entity but only part of a large and more complex spontaneous preterm birth syndrome. 
Cervical insufficiency usually occurs during the middle of the second or early third trimester, depending upon the severity of insufficiency. Cervical incompetence may be congenital or acquired. The most common congenital cause is a defect in the embryological development of Mullerian ducts. In Ehlers-Danlos syndrome or Marfan syndrome, due to the deficiency in collagen, the cervix is not able to perform adequately, leading to insufficiency.
The most common acquired cause is cervical trauma such as cervical lacerations during childbirth, cervical conization, LEEP (loop electrosurgical excision procedure), or forced cervical dilatation during the uterine evacuation in the first or second trimester of pregnancy.
Epidemiologic studies suggest an approximate incidence of 0.5% in the general obstetric population and 8% in women with a history of previous mid-trimester miscarriages. Wide variation in the incidence of cervical incompetence has been reported, which is likely due to real biologic differences among the study population, the criteria used to establish the diagnosis, and reporting bias between general practitioners and referral centers.
The competent human cervix is a complex organ that undergoes extensive changes throughout gestation and parturition. A complex remodeling process of the cervix occurs during gestation, involving timed biochemical cascades, interactions between the extracellular and cellular compartments, and cervical stromal infiltration by inflammatory cells. Any disarray in this timed interaction could result in early cervical ripening, cervical insufficiency, and preterm birth or miscarriage. Current evidence suggests that cervical incompetence functions along with a continuum that is influenced by both endogenous and exogenous factors, such as uterine contraction and decidual/membrane activation. 
Cervical insufficiency is a well -recognized cause of late miscarriage, and the diagnosis is often made retrospectively after a woman has had a second-trimester loss. Most of the women have no symptoms or only mild symptoms beginning in the early second trimester. These include abdominal cramping, backache, pelvic pressure, vaginal discharge which increases in volume, vaginal discharge which changes from clear to pink, and spotting. 
The diagnosis of incompetent cervix is usually made in three different settings:
The digital or speculum examination reveals a cervix that is dilated 2 cm or more, effacement greater than or equal to 80%, and the bag of waters visible through the external orifice (os) or protruding into the vagina. The diagnosis is frequently made on the basis of history retrospectively after multiple poor obstetrical outcomes have occurred.,
Cervical incompetence is primarily a clinical diagnosis characterized by recurrent painless dilatation and spontaneous midtrimester birth, usually of a living fetus. The presence of risk factors for structural cervical weakness supports the diagnosis. The challenges in making the diagnosis are that relevant findings in prior pregnancy are often not well-documented and only a subjective assessment.
Most of the earlier reported tests for cervical incompetence including hysterosalpingography and imaging of balloon traction on the cervix radiographically, assessment of the patulous cervix with Hegar or Pratt dilators, balloon elastance test, and graduated cervical dilators which are used to calculate a cervical resistance index were based on the functional anatomy of the internal os in the non-pregnant state are of historical interest and because none have been validated, none of these tests are in common use.
The diagnosis of cervical insufficiency is challenging because of the lack of objective findings and clear diagnostic criteria. Cervical ultrasound has emerged as a proven, clinically useful screening and diagnostic tool in the selected population of high-risk women based on an obstetrical history of a prior (early) spontaneous preterm birth. The transvaginal ultrasound typically shows a short cervical length, less than or equal to 25 mm, or funneling, ballooning of the membranes into a dilated internal os but with the closed external os.
Many nonsurgical and surgical modalities have been proposed to treat cervical insufficiency. Certain nonsurgical approaches, including activity restriction, bed rest, and pelvic rest have not proven effective in the treatment of cervical incompetence and their use is discouraged. Another nonsurgical treatment to be considered in patients at risk of cervical insufficiency is the vaginal pessary. The evidence is limited for a potential benefit of pessary placement in select high-risk patients. ,
Surgical approaches include transvaginal and transabdominal cervical cerclage. The two types of this commonly used vaginal procedure include McDonald and modified Shirodkar. McDonald involves taking four or five bites of number 2 monofilament suture as high as possible in the cervix, trying to avoid injury to the bladder or the rectum, with a placement of a knot anteriorly to facilitate the removal. The Shirodkar procedure involves the dissection of the vesical-cervical mucosa in an attempt to place the suture as close to the cervical internal os as close, otherwise, as possible. The bladder and rectum are dissected from the cervix in a cephalad manner, the suture is placed and tied, and mucosa is replaced over the knot. Nonresorbable sutures should be used for cerclage placement using the Shirodkar procedure.
During an emergency, the cerclage patient is placed in Trendelenburg position and a bag of membranes is deflected cephalad back into the uterus by placing a Foley catheter with a 30 mL balloon through the cervix and inflating it. The balloon is deflated gradually as the cerclage suture is tightened. ,
Transabdominal cerclage with the suture placed at the uterine isthmus is used in some cases of severe anatomical defects of the cervix or cases of prior transvaginal cerclage failure. It can be performed laparoscopically, but it generally requires laparotomy for initial suture placement and subsequent laparotomy for removal of the suture, delivery of the fetus, or both. ,