Cervicometry is a transvaginal ultrasound examination during pregnancy, the purpose of which is to measure the length of the cervix, assess the condition of the external and internal pharynx and cervical canal. Ultrasound of the cervix is informative for detecting isthmic-cervical insufficiency (ICI) and predicting the risk of spontaneous termination of pregnancy or premature birth. Standard cervicometry is performed at 18-22 weeks of pregnancy, however, if there are special indications, the study can be prescribed at an earlier date and repeated in dynamics. The length of the cervix depends on the gestational age and obstetric history, so ultrasound results should be evaluated in conjunction with these data.
Cervicometry (from Lat. “cervix uteri” – cervix and Greek “metreo” – to measure) is an ultrasound technique aimed at assessing the size and functional state of the cervix in pregnant women. Throughout the entire gestation period, the cervix serves as an anatomical barrier that holds the fetus in the uterus. Normally from about 35-36 weeks. pregnancy begins the process of gradual “maturation” of the cervix – its softening and shortening, expansion of the cervical canal, necessary for the normal course of the birth process. For various reasons, in some pregnant women, shortening and opening of the cervix occurs prematurely, which can result in premature birth. That is why it is so important to monitor the condition of the cervix during pregnancy. The most accurate, safe and informative method today is ultrasound cervicometry.
Usually, the assessment of the state of the cervix in all pregnant women is performed during a planned screening ultrasound of the second trimester at a period of 18-22 weeks. If a woman has a burdened obstetric history, cervicometry can be performed starting from 11-13 weeks of pregnancy (optimally – during the first screening ultrasound). In case of detection of the threat of spontaneous termination of pregnancy, dynamic ultrasound of the cervix is repeated at intervals of 1-2 weeks.
First of all, cervicometry is indicated for women who are at increased risk of miscarriage:
- with signs of isthmic-cervical insufficiency (including with a circular suture applied to the cervix);
- having had pregnancies in the past that ended in a late miscarriage (at 13-27 weeks of pregnancy) or premature birth (earlier than 34 weeks of pregnancy);
- those who have previously undergone surgery on the cervix (for example, conization);
- having a deformity of the cervix due to previous medical abortions, traumatic childbirth, SDC;
- carrying multiple pregnancies.
Alarming symptoms that require immediate access to an obstetrician-gynecologist are heaviness in the lower abdomen, frequent urination, bloody discharge from the vagina. These signs can serve as formidable harbingers of termination of pregnancy. In such a situation, a pregnant woman may also be prescribed cervicometry.
Methodology of conducting
According to the accepted international standards of ultrasound diagnostics, cervicometry is performed by transvaginal access with an emptied bladder. Visualization of the cervix is also possible through the anterior abdominal wall, but in this case it is necessary to fill the bladder, which often overlaps the inner pharynx. Meanwhile, in order to accurately determine the length of the cervix, the measurement should be carried out strictly from the external pharynx to the V-shaped recess of the internal pharynx, which is possible only in conditions of transvaginal scanning.
Preparation for ultrasound of the cervix is not required. The procedure is performed in the position of a woman lying on her back with her legs bent at the knees. The ultrasound sensor is carefully inserted into the vagina, avoiding too much pressure on the cervix. The duration of the study should not exceed 2-3 minutes. During cervicometry, the dimensions of the cervix (length and width), the expansion of the cervical canal, the closeness of the internal pharynx, the presence and degree of prolapse of the fetal membranes into the internal pharynx are evaluated, if there is a seam on the cervix, its location and consistency.
Interpretation of results
The length of the cervix depends on the duration of pregnancy, the number of fetuses carried, the number of previous births. Normally, with a single pregnancy at 16-20 weeks, the length of the cervix is 4.5-4 cm; at 25-28 weeks, 4-3.5 cm; at 32-36 weeks, 3.5-3 cm. It is believed that with a cervical length of more than 3 cm, the risk of premature birth is less than 1% and is comparable to the general population. A neck < 2.5 cm long between 14 and 24 weeks of gestation is regarded as short; in this case, there is a high probability of premature birth at 36-37 weeks of pregnancy. With a cervical length <2 cm, the average gestational age of newborns is 34 weeks. The length of the cervix < 1.5 cm is associated with a high risk of premature birth at 34 weeks, and less than 1 cm – at 32 weeks of pregnancy.
If, according to the results of cervicometry, a threatening shortening of the cervix is established, the pregnant woman is hospitalized in the department of gynecology or pathology of pregnancy. Bed rest, complete physical and sexual rest are prescribed. In order to prevent spontaneous termination of pregnancy, intravaginal administration of progesterone may be prescribed. Also, from conservative methods, obstetric unloading pessaries are used, which are put on the cervix. The most radical method of correction of ICI is the imposition of a circular suture on the cervix (cervical cerclage) – this reduces the risk of premature birth by about a quarter.