Cervical Incompetence and Cerclage - 2 - An Overview of Cervical Structure
Tuesday, August 19, 2008
Kenneth F. Trofatter, Jr., MD, PhD
Although the cervix is contiguous with the body of the uterus, it is structurally different from the uterus in several key aspects. Both the uterine wall (the myometrium) and the cervix contain smooth muscle and fibrous connective tissue, but there is a much greater percentage of the connective tissue in the cervix than in the myometrium. The uterus is “designed” to contract and, when the time is right, eventually push the baby out, while the role of the cervix, under normal circumstances, is to keep the baby inside until it is mature enough to survive in the cold cruel world outside the womb.
The fibrous connective tissue of the cervix is mostly composed of types I and II collagen, elastin, and proteoglycans. The collagen is heavily ‘cross-linked’ and this imbues the cervix with a tremendous resistance, again under normal circumstances, to stretching and ‘softening’ until the biochemical cascade that progresses to labor ensues. At that point, the cervix is capable of undergoing a remarkably rapid transformation from a structure that has the consistency of a rubber eraser to the soft, compliant, elastic structure that will permit the relatively easy passage of the baby from the uterus and into the birth canal – a transformation that results from the remodeling (uncross-linking) of the collagen and the extracellular matrix.
The cervix, then, is a very dynamic organ that always has the innate ‘potential’ to change from barrier to facilitator of uterine evacuation. In cervical incompetence, some women probably do not have a normal percentage or configuration of the fibrous connective tissue, others may be overly sensitive, due to genetic susceptibility or metabolic abnormalities, to stimuli that would ordinarily not lead the “normal" cervix to undergo the transformations associated with premature cervical ripening, others may be exposed to higher levels of factors that can initiate cervical ripening independently of the innate pathways, and others may have congenital or iatrogenic diminution of normal ‘integrity’ at the internal os that leads to subclinical cervical changes that eventually result in activation of the innate ‘ripening’ pathways or to ascending infection that can promote more rapid cervical change and/or premature uterine contractions. Then of course, there may be individuals who have more than one of these predisposing factors...
Labels: cervical incompetence, cervical insufficiency; premature labor
4 Comments:
At Wed Aug 27, 04:36:00 PM 2008,
Becky said…
Dear Dr T,
I lost twins after delivering them at exactly 24 weeks, they lived for nine days. I conceived them through ICSI IVF after my husband was diagnosed with low sperm count. I had many complications throughout the pregnancy including contractions starting around 16 weeks not painful, cervical shortening noticed around 18 weeks, and right before I delivered I was found to have a serious case of bacterial vaginosis, which had probably spread to the uterus. I had an emergency cerclage put in at 19 weeks, my cervix was already funneling and dilated. I am scared that this is when I developed the infection or it was already brewing because I was dilated. What do you think?
So my real question is my husband and I just found out that we are pregnant without any help of fertility meds, so very surprising to us. 1)Do you recommend a preventative cerclage at 13-14 weeks (my OB does)?or could my IC been secondary to infection and twins? 2)Should I be put on prophylactic antibiotics for the duration of my pregnancy? 3)Do I need progesterone shots with this pregnancy? (last one I did)
Thanks for all your help!
At Wed Sep 03, 06:25:00 AM 2008,
Kenneth F. Trofatter, Jr., MD, PhD said…
To Becky: First of all, I am so sorry for your loss. With regard to your questions, I can tell you what I would suggest. You have one of the big risk factors in my book for cervical incompetence - infertility. Secondly, you had premature cervical changes very early in the pregnancy, even if it was twins. Thirdly, you may have a tendency to be one of the folks who chronically harbors BV. All those things put you at increased risk for cervical incompetence and/or premature labor and delivery. I would suggest a cerclage at 13 weeks after having had first trimester screening for aneuploidy. I would then follow you still with serial cervical ultrasounds between 18 and 24 weeks. At the first sign of BV, I would place you on metronidazole 2-3 times daily and continue it until you got through midtrimester and I would give some thought to 17-OH-P since there is some evidence progesterne helps "quiet the uterus" and delays delivery in individuals with a short cervix. You will find others who will disagree with me on one or more of these points, but that's how I would handle things! Good luck. Dr T
At Wed Nov 12, 06:47:00 PM 2008,
Rizwan said…
Hi Dr. T,
Firstly many thanks for doing such good work and helping women better understand such precious loss.
I am curious to find out why you believe infertility is a big risk factor for incompetent cervix.
Thank you,
Saadia
At Thu Nov 27, 05:39:00 PM 2008,
Kenneth F. Trofatter, Jr., MD, PhD said…
To Saadia: I have had to care for many infertility patients after they have successfully conceived, and even in the singleton pregnancies, they appear to be at greater risk for cervical incompetence. I have no idea why that is - perhaps it is related to hormonal imbalances or to insulin resistance since so many of these women have polycystic ovary syndrome, at least in the populations for which I have cared, and they seem to be at the greatest risk. In some instances it may be related to congenital or iatrogenic uterine abnormalities. Thanks for writing and I wish I had the answer for you.
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