Cervical Insufficiency: The Diagnosis
- Cervical insufficiency (CI) is asymptomatic cervical dilatation in second and third trimester of pregnancy.
- Consequently, amniotic membranes can protrude into the cervical canal, leading to further cervical dilatation, membrane rupture and PD.
- In the absence of therapeutic intervention, this condition is likely to reoccur in every subsequent pregnancy.
- After 14 weeks of pregnancy, we do have the possibility to recognize asymptomatic changes suggestive of CI.
- These changes are detectable by cervical assessment using transvaginal ultrasound—so called cervical measurement or cervicometry (CM).
- CM can provide important information about the cervical condition and changes in pregnancy.
- It should be performed in all women at risk for CI starting from 14 weeks.
- Earlier examination is of no particular use as uterine cervix acting as a sphincter is not fully formed.
- Although, if performed earlier, it helps in identification of cases of habitual abortion due to cervical incompetence.
- The examination should be repeated in two weeks intervals finishing at 24 weeks.
Cervical insufficiency in Ultrasound
- CM can directly visualize uterine cervix including internal and external cervical os.
- It can display the shape of the cervix and present different planes for the measurements of all cervical segments.
- Two ultrasound based criteria are found to be related to cervical insufficiency.
- Length of the closed part of the cervical canal,
- Shape of the internal cervical os (“T”, or “Y”, or “V” with “funneling”).
- Normal values for cervical length are 25 mm and more.
- Cervical length shorter than 25 mm and “funneling” above 25%, cerclage does not significantly improves pregnancy outcome.
- Funneling is the relationship of the dilatation of internal cervical os and closed part of the cervical canal.
- Length of the closed part <15 mm, cerclage does not reduce the incidence of LM and PL, but significantly increases the risk of PPROM.
- Length of the closed part between 15 and 25 mm there are clear signs of CI yet the prolapsed membranes are extremely rare (liable for selective cerclage).
- If prolapsed membranes in the cervical canal and the length of the closed part of the cervix shorter than 15 mm there is 50% risk of PL with high perinatal mortality.
Route of Ultrasound Scan
- Transvaginal ultrasound was found to be significantly better than abdominal, as there is no need for full urinary bladder which might change anatomical relationships and change the shape of the cervix.
As well as in the diagnosis of CI ultrasound can be used in the further assessment of the women with cerclage.
- The stitch can clearly be seen on ultrasound examination and allows the assessment of the placement and potential further changes on the cervix in ongoing pregnancy.
- This may be of help in identifying patients at higher risk for premature rupture of the membranes and preterm delivery.
Never forget the cervix whenever you are scanning an obstetric case.