The Incompetant Cervix
Vol.1 No.3 

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The Incompetent Cervix 

With advancing fetal age, the expanding volume of the uterus places increasing forces upon the cervix. In the normal pregnancy, the cervix maintains significant strength to resist these forces upon dilation and effacement usually through the second and early third trimester. Certain conditions predispose the cervix to premature dilation and effacement and this in turn can lead to premature labors and pregnancy losses. When this event of premature dilation and or effacement of the cervix occurs, it is presumed a consequence of weakened cervical tissue fibers and is therefore been called "The Incompetent Cervix." The incompetent cervix accounts for approximately 15 per cent of all second trimester losses. The most common etiologies or predisposing factors for an incompetent cervix are: 1. Maternal DES exposure 2. Prior conization biopsy of the cervix 3. Repeated dilation of the cervix 4. Traumatic injuries to the cervix 1. DES or diethylstilbestrol is a synthetic estrogen which was given to women in the 1950's and 1960's with the hope of preventing repeated miscarriages. It was discovered however in the early 1970's that the daughters of these women as they entered their teenage years were developing abnormalities of the cervix called adenosis and rarely, adenocarcinoma(cancer) of the vagina- an extremely rare form of cancer

Although most of the changes of adenosis are benign, women, as they enter their reproductive years have a higher incidence of infertility and miscarriage- particularly in the mid-trimester. The adenosis which affects the morphology of the cervix weakens its inherent strength resulting in an incompetent cervix. Most women however who are DES exposed do not have this problem but the history of DES exposure is very important so that pregnant "DES daughters" may be followed more closely. 2. Conization biopsy of the cervix is a procedure which is performed to diagnose and treat cancerous or pre-cancerous changes in the cervix. The procedure actually excises a large portion of the cervix which contains the abnormal(dysplastic) cells and in doing this, almost invariably removes a portion of the muscular and connective tissue fibers of the cervix which contributes to its weakening.

Newer techniques such as laser therapy and electrical loop excision therapy can theoretically reduce the amount of tissue distruction but should still be taken into consideration when evaluating a patients history. 3. Patients who have undergone multiple therapeutic abortions and dilation of the cervix are at increased risk for an incompetent cervix because the muscle and connective tissue fibers of the cervix can loose their elastic properties and remained stretched if dilation of the cervix with mechanical dilators is performed multiple times. The appropriate treatment for these patients is "expectant" by means of frequent cervical examinations in the mid trimester.

The diagnosis of the incompetent cervix is not an exact methodology. Examinations early in the second trimester are important in any women with a history of any of the above listed factors or any women with a history of an unexplained mid trimester loss., particularly if it occurred without much pain or bleeding-the so called "silent dilation of the cervix. Early diagnosis of premature dilation of the cervix can lead to therapy which can sustain the pregnancy through and beyond the period of viability. Ultrasound examinations of cervical length and thickness can also be helpful but its role is not as well defined. Should the cervix be found to be dilated or particularly thinned(effaced) a suture can be placed around the cervix and tied to give the cervix strength. This is called a cervical cerclage. The two most utilized techniques for cervical cerclage are the Shirodkar and the McDonald procedures. Both yield similar results and their different uses depend mostly on the training and experiences of the operating surgeons. The premise for the cerlage is to further close the cervix and reinforce the connective tissue with high tensile-strength suture so as to maintain the integrity of the pregnancy. The procedure is most commonly performed just after the first trimester and can be performed as an outpatient under regional(spinal or epidural) or general anesthesia. Although this provides a strength to the already weakened cervix, the therapy for incompetent cervix must also include bed rest-sometimes throughout the pregnancy, possible use of tocolysis(the process of stopping labor with medications) and hospitalization when needed. In the appropriately selected population, cervical cerclage can be very effective and yield an excellent prognosis for term or near term delivery. 

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