Cervical insufficiency (previously known as cervical incompetence) is defined as the inability of the cervix to retain the pregnancy, which then result in painless cervical dilatation or pregnancy loss in the absence of uterine contractions. This occurs in 1% of all pregnancies, and in as many as 20% of mid second trimester spontaneous pregnancy losses.
There are some conditions that predispose to cervical insufficiency. These include:
1. Trauma or injury to the cervix associated with a prior delivery, miscarriage or previous surgery to the cervix or uterus
2. Congenital uterine anomalies
3. Intrinsic deficiencies in cervical collagen and elastin.
The cervix is usually firm and composed of collagen that plays an important role in protecting the pregnancy. Therefore, any condition that degrades collagen may enhance the softening of the cervix and later lead to cervical dilation.
The diagnosis of cervical insufficiency is usually made in one of a few different ways:
1. A history of pregnancy losses between 12-23 weeks gestation that are characterized by painless cervical dilatation
2. Transvaginal ultrasonography showing a very short cervical length at 20 weeks pregnancy
3. Painless dilatation of the cervix and / or prolapse amniotic membrane at the vagina or out of the vagina in this current pregnancy
1. Bed rest and activity restriction
2. Vaginal progesterone for cervix length less than or equal to 25 mm reduces the risks of preterm birth.
3. Cervical Cerclage before 24-26 weeks may prolong pregnancy with a diagnosis of cervical insufficiency. This is a stitch on the cervix performed usually under regional anaesthesia by an obstetrician experienced in such procedures.
Cervical cerclage is a surgical operation performed to close up / lengthen the cervix (which is the door to the opening of the uterus or womb). This is performed in the second trimester (usually between 12-24 weeks) with the aim to reduce the risk of second trimester miscarriages from cervical insufficiency or severe premature delivery.
Cervical cerclage may be considered in one of the following conditions:
Past history of a pregnancy with PAINLESS dilatation of the cervix with eventual miscarriage from 12 weeks onwards. This would be highly suggestive of cervical incompetence.
Past history of 3 or more midtrimester (12-24 weeks) losses or spontaneous preterm births (24-36 weeks).
Short cervix < 25 mm with a history of one or more midtrimester (12-24 weeks) loss / spontaneous preterm birth (24-36 weeks)
Severely short cervix <= 15 mm on scan at the second trimester scan.
Shortening cervix to <=15 mm on scan <= 24 weeks despite treatment with vaginal micronized progesterone pessaries.
Physical examination that shows painless dilatation of the cervix <= 24 weeks
Risks of cervical cerclage:
Infection causing miscarriage or preterm labour
Rupture of amniotic membrane - either from the inadvertent suturing of the membranes during the cerclage procedure or from infection after the procedure
Less common risks include cervical laceration (i.e. if tearing from the suture occurs during labour before the suture has been removed) and cervical dystocia (i.e. inability of the cervix to dilate normally during labour because of the scarring caused by the suture)
Rarely, it may not be possible to complete the cervical cerclage from the transvaginal approach if the cervix is so short that it is flushed with the rest of the vaginal vault.
Transvaginal approach - this is the main approach for cervical cerclage. The commonest method used for cervical cerclage is known as the McDonald's cerclage. This is the approach with the lowest risks of the surgery and is the preferred method in most cases.
Transabdominal approach - this may be the method of choice if previous transvaginal cerclage operations have failed or cannot be performed as the cervix is already flushed with the vaginal vault. This method is associated with higher risks as it involves either an open abdominal incision or a laparoscopic (or keyhole) approach. This is rarely performed.