B20. Cervical incompetence; etiology, diagnosis and therapy
Cervical insufficiency or cervical incompetence is a condition where the cervix fails to retain a pregnancy in the second trimester due to painless shortening and dilation of the cervix. This is recurrent (occurs across multiple pregnancies) and may lead to spontaneous abortion or preterm birth. In physiological cases, the cervix remains long and closed during pregnancy until labour.
Approximately 10% of cases of preterm labour is due to cervical insufficiency.
Etiology
Known risk factors include:
- Previous cervical trauma (labour, treatment of cervical lesions)
- History of short cervical length
- History of preterm birth or second trimester abortion
- Congenital abnormalities (collagen disorders (EDS), exposure to DES, uterine abnormalities)
However, most cases are idiopathic and occur without any identifiable risk factor.
Pathomechanism
Some sort of structural cervical weakness makes the cervix too weak to withstand the downward pressure on the cervix from the uterine cavity when it becomes too large, which occurs during the second trimester.
Clinical features
The condition is asymptomatic and painless and occurs in the absence of uterine contractions.
Diagnosis and evaluation
Physical examination may reveal a dilated and effaced cervix. Asking the patient to perform the Valsalva manoeuvre may cause foetal membranes to prolapse into the endocervical canal or the vagina.
Ultrasound allows us to measure the cervical length, which is usually less than normal (< 25 mm) in case of cervical insufficiency.
Nowadays, we measure the cervical length routinely during routine ultrasound examination. Only a few of those with short cervix develop cervical insufficiency, but a diagnosis of short cervix should be followed up by more frequent monitoring or progesterone supplementation.
When I had this topic on my exam, the examiner said that it was obligatory to make a culture (of what exactly? Urine and vaginal swab, perhaps) before performing the cerclage, but UpToDate disagrees, so.
Treatment
A cervical cerclage is a surgical procedure used to support the cervical structure. Surgical suture is used to reinforce the cervix. The procedure may be performed transvaginally (most frequent) or transabdominally and is usually performed in weeks 12 – 14. There are two methods of transvaginal cerclage, McDonald’s method and Shirodkar’s method. The cerclage is later removed at week 36 – 37 or after preterm labour has occurred.
Supplementation of progesterone vaginally may also be used as an addition to cerclage. If short cervix is diagnosed (but insufficiency has not developed), progesterone supplementation is recommended to reduce the risk of insufficiency.
Apparently there’s a surgical procedure which can be performed to prevent cervical insufficiency, but it must be performed before pregnancy. It involves cutting out a piece of the anterior wall of the cervix and suturing it, which forms a scar which strengthens the cervix. I don’t know what it’s called, and I can’t find anything about it when searching, but my examiner mentioned it on my exam.
Some advocate for limiting work, exercise, and coitus. Strict bed rest is known to not be efficacious and is not recommended.
There is only weak, absent, or contradictory evidence for the efficacy of cervical cerclage and limiting work, exercise, and coitus.
Complications
- Preterm birth
- Second trimester pregnancy loss