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StorkNet's Week By Week Guide to Pregnancy
Diagnosing and Treating Incompetent Cervix
Geoffrey Sher, M.D.
Q.I delivered my baby early prematurely. My water broke before I even felt contractions. I am aware that the cause for her early birth will never be known. My fear in future pregnancies is that my cervix will dialate unbeknownst to me and I'll have another premature birth. How can I be sure I don't have a weak cervix and what I can do if I have one?
A. The important thing is to exclude cervical incompetence because this is the most common cause of "passive cervical dilatation." The diagnosis of cervical incompetence is usually strongly suspected on the basis of the following history:
- Recurrent second trimester miscarriages or premature births, in which both bleeding and painful contractions are minimal and the process is completed rapidly
- Few prior warning symptoms or signs
- Where the bag of bulging membranes often breaks followed by a sudden gush of water per vagina that heralds the onset of miscarriage or premature birth
- A physician inadvertently detects a partially dilated and shortened cervix with routine pelvic examination performed in the mid-trimester of pregnancy.
Once the diagnosis of cervical incompetence is suspected, it can and indeed should be confirmed on the basis of one or more of the following:
- A hysterosalpingogram (HSG-dye x-ray test) to evaluate for a well demarcated anatomical transition from endocervical canal to the uterine cavity (without evidence of "funneling") and to detect a deformity (congenital or acquired) of the uterus, that can also lead to mid-trimester miscarriage and premature birth.
- A vaginal ultrasound examination to measure the length of the cervical canal (it should measure more than 2.5 cm) and to exclude pathology of uterine wall(e.g.; fibroids)
- A diagnostic hysteroscopy to carefully evaluate uterine scarring, fibroid tumors protruding into or distorting the uterine cavity and for the congenital deformities such as a uterine septum.
Cervical incompetence is routinely treated by the placement of a temporary circumferential non-absorbable tape or suture around the neck of the cervix at the 12th-14th week of pregnancy per vagina ("McDonald cerclage"). The advantage of this approach is that the cerclage can readily be removed a week or two before delivery, thereby allowing a subsequent spontaneous vaginal birth to take place The disadvantage of placing a McDonald cerclage is the ever present risk of puncturing the fetal membranes while inserting the stitch. This sometimes prompts the overcautious OB/GYN to place the stitch well below the cervical-uterine junction, thereby increasing the likelihood that it will slip or tear and thus fail to prevent cervical shortening and dilatation.
After undergoing a preliminary assessment to confirm the diagnosis of cervical incompetence, non-pregnant women in whom a McDonald cerclage has failed, should be considered for the elective placement of a permanent, non-absorbable cerclage "Shirodkar suture," prior to undertaking another pregnancy. In fact, we believe that this should be considered as the primary (initial) approach. The reason is that in the absence of a pregnancy, it is possible, through careful surgical dissection, to ensure the correct placement of the suture (usually a double strand of #2 nylon is used), and in so doing, maximize its effectiveness. The one relative disadvantage to this approach is that the completely buried Shirodkar suture, is sometimes not amenable to removal before delivery. Accordingly, such women would require delivery by Cesarean section. Notwithstanding this, we hold that a Cesarean delivery, is a relatively small price for a woman who has usually experienced recurrent pregnancy loss, and/or repeated premature deliveries, to pay to have a healthy baby.
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