Cerclage to Prevent Preterm Birth in Mothers with a Short or Incompetent Cervix

The cervix is the part of the womb that connects to the vagina.  Before pregnancy, it is closed and rigid.  As pregnancy progresses, the cervix begins to soften.  Normally, the cervix thins and opens in response to contractions during the onset of labor.  When the mother has an insufficient cervix, the pressure in the womb can cause the cervix to open too soon, allowing the membranes to fall through the cervical opening. These membranes eventually rupture, leading to preterm labor or miscarriage.  Incompetent or insufficient cervix, is thought to cause as many as 20 – 25% of premature deliveries in the second trimester.

Determining if the mother’s cervix is shortening is part of most assessments for incompetent cervix.  However, short cervical length is actually a marker for premature birth rather than incompetent cervix.  Both short cervix and incompetent cervix can be treated with cervical cerclage, and experts agree that it is a very effective form of treatment.

A cervical cerclage is a stitch placed through the mother’s cervix during pregnancy. The main goal of a cervical cerclage is to reinforce the cervix, but lengthening of the cervix is a secondary effect.

When a mother receives a cervical cerclage, the surgery usually entails closing the cervix through the vagina.  Another approach involves performing the cerclage through an abdominal incision in a procedure called a transabdominal cerclage.  Transabdominal cerclage makes it possible to place the stitch exactly at the level that is needed.  It can be carried out when the cervix is very short, effaced, or totally distorted.

Cerclages are usually performed between weeks 14 and 24 of the pregnancy.  If a mother had a premature birth that may have been caused by cervical incompetency, the physician might recommend prophylactic cervical cerclage for the next pregnancy, before the cervix begins to open. This procedure is typically done before week 14 of pregnancy, although it can be performed later.  Sutures are removed between weeks 36 and 38 to avoid problems during labor. They are also removed if the mother has ruptured membranes and evidence of an infection (e.g., chorioamnionitis).  Cerclage may not be recommended if:

• A mother has increased cervical irritation,
• Her cervix has dilated 4 centimeters, or
• Her membranes have ruptured.

A physician will typically recommend a cervical cerclage for:

• Mothers with cervical incompetence based on a prior second trimester losses and/or a premature birth.  This is a “history-indicated” cerclage, and it is usually placed at 12 – 14 weeks of gestation.
• Mothers pregnant with one baby and a short cervical length (<25 mm) on transvaginal ultrasound exam at 14 – 24 weeks of gestation.  This is an “ultrasound-indicated” cerclage.
• Mothers with cervical incomptence based on a dilated cervix on a digital or speculum exam at 16 – 24 weeks of gestation (cervix is opening).  This is a “physical exam-indicated” cerclage.

A cerclage is not placed if:

• The mother is in active labor
• The mother has a placental abruption or infection
• The mother has preterm premature rupture of the membranes (PPROM).

In the case of cerclages that aren’t scheduled in advance, experts recommend close observation of the mother for an hour prior to surgery to make sure these conditions are not present.  Other contraindications to cerclage placement include fetal membranes protruding through the the cervix and any active bleeding.

There are many conditions and events that can cause an incompetent cervix. These include the following:

• Obstetric trauma: If a woman has experienced a cervical tear during a previous delivery, she could have an incompetent cervix.
• Certain cervical procedures: Various surgical procedures — including a procedure used to take a sample of cervical tissue (biopsy) and a treatment that uses an electrical current to remove diseased tissue from the cervix (loop or LEEP procedure) — can cause cervical insufficiency.
• Dilation and curettage (D & C): D & C is used to diagnose or treat various uterine conditions or to clear the uterine lining after a miscarriage or abortion.  It can cause damage to the cervix.
• In-utero exposure to diethylstilbestrol (DES):  DES is a synthetic form of estrogen, and exposure to this during pregnancy is associated with cervical incompetence.
• Uterine abnormalities and deficiencies in cervical collagen and elastin.

Anything that can cause cervical weakness is a serious risk factor for cervical incompetence. Specifically, risk factors for incompetent cervix include:

• A previous diagnosis of cervical incompetency during pregnancy
• Previous preterm premature rupture of membranes (PPROM)
• A cervical biopsy
• A torn cervix from a previous trauma during delivery
• Repeated or late-term abortion
• Abnormalities of the uterus
• D & C procedures

It is important that medical professionals are aware of risk factors a mother may have for cervical incompetency so that treatment, such as cerclage, can be initiated if necessary.  Short cervix is the most important indication for a cerclage, and physicians are expected to determine the mother’s cervical length between weeks 14 and 24 of pregnancy.

If any of the risk factors for an incompetent cervix exist, the physician should review the woman’s history and perform a physical exam and ultrasound tests to determine cervical length.  Methods for diagnosing an incompetent cervix include the following:

• History:  An important indicator of cervical insufficiency is if the mother had a miscarriage or preterm birth between the fourteenth and twenty eighth week (approximately) of a previous otherwise-uneventful pregnancy.  Other important questions for a physician to investigate are whether the mother has a history of DES exposure or congenital cervical weakness, and whether she has had prior trauma to the cervix from D & C procedures or cone biopsies.
• Physical exam:  A manual pelvic exam of the cervix during the second or third trimester can reveal partial opening of the cervix with shortening and thinning of the vaginal part of the cervix, which would indicate cervical weakness.
• Tests:  The physician should perform serial transvaginal ultrasound studies (TVS) after the sixteenth week in a mother with a history suggesting cervical incompetence. Vaginal ultrasounds can help monitor the cervical length and determine if the cervix is opening. Ultrasound studies determine the length of the cervix; in a compromised cervix, the length may be shortened.

The hormone progesterone is another treatment for short cervix.  When given vaginally, progesterone helps prevent premature birth in mothers at risk of preterm labor due to a short cervix.  If contractions occur too early the mother may go into premature labor; progesterone helps keep the uterus from contracting and helps the uterus grow. Progesterone therapy is usually initiated around the 16^th – 20^th week of pregnancy, lasting until the 36^th week.

This type of therapy is given to the mother every week via intramuscular injection. It is typically given when the mother had preterm labor in the past and the physician thinks she is at risk for having preterm labor in her current pregnancy. In the case of short cervix, progesterone is usually given vaginally at the 18^th week of pregnancy. Some physicians also give progesterone therapy to mothers pregnant with twins.  Mothers pregnant with twins can have progesterone therapy if they have a short cervix or have had a previous preterm birth.  In addition, mothers who have had previous PPROM appear to benefit from progesterone therapy in later pregnancies.

When a mother has a history of premature birth, many physicians begin carefully monitoring the length of her cervix by performing serial ultrasounds every week, from week 15 – 24 of pregnancy.  If her cervix begins to open or become shorter than a certain length, cerclage or progesterone will typically be recommended.

Progesterone and cervical cerclage are key treatments for the prevention of preterm birth. In fact, these are the only two treatments that have proven effective in significantly reducing the incidence of preterm birth.

When a baby is born prematurely – or about to be born prematurely – physicians must make every effort to prevent the serious problems associated with preterm birth, such as respiratory distress, sepsis, brain bleeds, and PVL.  When a baby is about to be born prematurely, corticosteroids should be given to the mother to help the baby.  Betamethasone is most commonly used.

Betamethasone  has been shown to reduce the incidence and severity of respiratory distress syndrome (RDS), intraventricular hemorrhages (brain bleeds), sepsis, and periventricular leukomlacia (PVL).  When appropriately given to the mother, corticosteroids help the baby’s lungs mature before the baby is delivered.  The drugs also help in the maturation of numerous other tissues throughout the baby’s body.

Magnesium sulfate can also be given when a baby is about to be born prematurely. This medication is given while the baby is in the womb, and it has direct and indirect effects on the baby’s brain.

Premature babies are at an increased risk for brain injury and cerebral palsy.  Magnesium sulfate helps protect the baby’s brain from injury and increases the chance that the baby will be born free of cerebral palsy.  It also decreases the risk of the baby developing other major movement disabilities such as severe motor dysfunction. Magnesium sulfate:

• Increases cerebral (brain) blood flow
• Has antioxidant effects
• Reduces the damaging molecules (cytokines) that are released when inflammation is present
• Reduces a process called neuronal excitability (excitotoxicity), which is damaging to the brain and occurs when the brain experiences trauma, restricted blood flow, and oxygen deprivation
• Stabilizes membranes in the brain
• Prevents large blood pressure fluctuations