宫颈分解剖学内口与组织学内口，它们之间有一子宫峡部相隔，宫颈管正常长度为2.5-3cm,当做妇科检查时，宫颈内口能顺利通过7号扩宫棒，或妊娠期无明显腹痛而B超测内口宽度>0.5cm,宫颈管长度<2.5cm,有助于诊断。从妊娠第4～5个月易发生。

　　The cervix is divided into anatomy, internal mouth and histological inner mouth. There is a hysterectomy between them. The normal length of the cervix is 2.5-3cm. When used as a gynecological examination, the cervix can successfully pass through the 7th expansion stick. Or there is no obvious abdominal pain during pregnancy and B ultrasound internal width & GT; 0.5 cm, cervical tube length & lt; 2.5 cm, which is helpful for diagnosis. From the 4th to 5th month of pregnancy.