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Cervical weakness also called cervical incompetence or cervical insufficiency is a medical condition of pregnancy in which the cervix begins to dilate (widen) and efface (thin) before the pregnancy has reached term. Definitions of cervical weakness vary, but one that is frequently used is the inability of the uterine cervix to retain a pregnancy in the absence of the signs and symptoms of clinical contractions, or labor, or both in the second trimester. Cervical weakness may cause miscarriage or preterm birth during the second and third trimesters. It has been estimated that cervical insufficiency complicates about 1% of pregnancies and that it is a cause in about 8% of women with second-trimester recurrent miscarriages.[rx]
Cervical insufficiency is the inability of the cervix to retain the fetus, in the absence of uterine contractions or labor (painless cervical dilatation), owing to a functional or structural defect. It is a 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.
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. [rx]
Causes of Cervical Weakness
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.
- However, in most patients, cervical changes are the result of infection/inflammation, which causes early activation of the final pathway of parturition. [rx],[rx]
- Abnormally formed uterus or cervix.
- Previous cervix surgery.
- Short cervix.
- Damaged uterus from previous miscarriage or childbirth.
- Exposure to diethylstilbestrol (DES), a synthetic (human-made) hormone given to some women in the past to help them have successful pregnancies.
Most women with cervical insufficiency do not have risk factors; however, the following risk factors have been identified:
- Congenital disorders of collagen synthesis (eg, Ehlers-Danlos syndrome
- Prior cone biopsies (particularly when ≥ 1.7 to 2.0 cm of the cervix was removed)
- Prior deep cervical lacerations (usually secondary to vaginal or cesarean delivery)
- Prior excessive or rapid dilation with instruments (now uncommon)
- Müllerian duct defects (eg, bicornuate or septate uterus)
- ≥ 2 prior fetal losses during the 2nd trimester
- Short cervical length
- Prior miscarriage
- Prior preterm delivery
- Prior D&C procedure (dilation and curettage), which is a procedure used to clear the uterine lining after a miscarriage or pregnancy termination. It can also be used to diagnose and treat certain uterine conditions.
- Prior loop electrosurgical excision procedure (LEEP) to remove abnormal/potentially cancerous cells from the cervix.
- History of other surgical procedures involving the cervix
- Diagnosis of the incompetent cervix in a previous pregnancy
- Twins or multiples pregnancy
- Injury from previous childbirth (obstetric trauma) during which the cervix was torn
- Repeated or late-term abortion
- Uterine abnormalities and anomalies
- Exposure to the drug diethylstilbestrol (DES), a synthetic form of the hormone estrogen
Symptoms of Cervical Weakness
If you have an incompetent cervix, you may not have any signs or symptoms during early pregnancy. Some women have mild discomfort or spotting over the course of several days or weeks starting between 14 and 20 weeks of pregnancy.
Be on the lookout for:
- A sensation of pelvic pressure
- A new backache
- Mild abdominal cramps
- A change in vaginal discharge
- Light vaginal bleeding
Diagnosis of Cervical Weakness
History and Physical
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. [rx]
The diagnosis of the incompetent cervix is usually made in three different settings:
Women who present with a sudden onset of symptoms and signs of cervical insufficiency
Women who present with a history of second-trimester losses consistent with the diagnosis of cervical incompetence (history-based)
Women with endovaginal ultrasound findings consistent with cervical incompetence (ultrasound diagnosis)
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.[rx],[rx]
Cervical incompetence is primarily a clinical diagnosis characterized by recurrent painless dilatation and spontaneous mid-trimester 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 those relevant findings in prior pregnancy are often not well-documented and only a subjective assessment.
Tests and procedures to help diagnose an incompetent cervix during the second trimester include:
- Transvaginal ultrasound – Your doctor may use transvaginal ultrasound to evaluate the length of your cervix and to check if membranes are protruding through the cervix. During this type of ultrasound, a slender transducer is placed in your vagina to send out sound waves that generate images on a monitor.
- Pelvic exam – Your doctor will examine your cervix to see if the amniotic sac has begun to protrude through the opening (prolapsed fetal membranes). If the fetal membranes are in your cervical canal or vagina, this indicates cervical insufficiency. Your doctor will also check for contractions and, if necessary, monitor them.
- Lab tests – If fetal membranes are visible and an ultrasound shows signs of inflammation but you don’t have symptoms of an infection, your doctor might test a sample of amniotic fluid (amniocentesis) to diagnose or rule out an infection of the amniotic sac and fluid (chorioamnionitis).
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.
Treatment of Cervical Weakness
Many non-surgical 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. [rx],[rx]
Treatments for or approaches to managing an incompetent cervix might include:
- Progesterone supplementation – If you have a history of premature birth, your doctor might suggest weekly shots of a form of the hormone progesterone called hydroxyprogesterone caproate (Makena) during your second and third trimester. However, further research is needed to determine the best use of progesterone in cervical insufficiency.
- Repeated ultrasounds – If you have a history of early premature birth, or you have a history that may increase your risk of cervical insufficiency, your doctor might begin carefully monitoring the length of your cervix by giving you ultrasounds every two weeks from week 16 through week 24 of pregnancy. If your cervix begins to open or becomes shorter than a certain length, your doctor might recommend cervical cerclage.
- Cervical cerclage – If you are less than 24 weeks pregnant or have a history of early premature birth and an ultrasound shows that your cervix is opening, a surgical procedure known as cervical cerclage might help prevent premature birth. During this procedure, the cervix is stitched closed with strong sutures. The sutures will be removed during the last month of pregnancy or during labor
Surgical approaches include transvaginal and transabdominal cervical cerclage. The two types of commonly used vaginal procedures 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. [rx],[rx]
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. [rx],[rx][rx][rx][rx][rx]