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Cervical incompetence (or cervical insufficiency) is a medical condition in which a pregnant woman's cervix begins to dilate (widen) and efface (thin) before her pregnancy has reached term. Definitions of cervical incompetence 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 incompetence may cause miscarriage or preterm birth during the second and third trimesters. Another sign of cervical incompetence is ''funneling'' at the internal orifice of the uterus, which is a dilation of the cervical canal at this location.〔(Cervical assessment ) from ''Fetal Medicine Foundation. Retrieved Feb 2014.〕 In a woman with cervical incompetence, dilation and effacement of the cervix may occur without pain or uterine contractions. In a normal pregnancy, dilation and effacement occurs in response to uterine contractions. Cervical incompetence occurs because of weakness of the cervix, which is made to open by the growing pressure in the uterus as pregnancy progresses. If the responses are not halted, rupture of the membranes and birth of a premature baby can result. According to statistics provided by the Mayo Clinic, cervical incompetence is relatively rare in the United States, occurring in only 1–2% of all pregnancies, but it is thought to cause as many as 20—25% of miscarriages in the second trimester. ==Diagnosis== Diagnosis of cervical incompetence can be challenging and is based on a history of painless cervical dilation usually after the first trimester without contractions or labor and in the absence of other clear pathology. In addition to history, some providers use assessment of cervical length in second trimester to identify cervical shortening using ultrasound. However, short cervical length has actually been shown to be a marker of preterm birth rather than cervical incompetence. Other diagnostic tests that have been suggested which have not been validated include hysterosalpingography and radiographic imaging of balloon traction on the cervix, assessment of the patulous cervix with Hegar or Pratt dilators, the use of a balloon elastance test, and use of graduated cervical dilators to calculate a cervical resistance index.〔 Normally, the cervix should be at least 30 mm in length. Cervical incompetence is variably defined. However, a common definition is a cervical length of less than 25 mm at or before 24 weeks of gestational age. The risk of preterm birth is inversely proportional to cervical length:〔(Cervical incompetence ) at Radiopedia. By Dr Praveen Jha and Dr Laughlin Dawes et al. Retrieved June 2014〕 *Less than 25 mm; 18% risk of preterm birth *Less than 20 mm; 25% risk of preterm birth *Less than 15 mm; 50% risk of preterm birth 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Cervical incompetence」の詳細全文を読む スポンサード リンク
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