Cervical Incompetence and Cerclage - 3 - Significance of the Internal Cervical Os
Saturday, August 23, 2008
Kenneth F. Trofatter, Jr., MD, PhD
Some of the potential risk factors for cervical incompetence include past obstetrical and family history of premature delivery and cervical incompetence, maternal obesity, congenital uterine abnormalities, uterine fibroids, previous uterine surgery (e.g., D&C, removal of uterine septum, myomectomy), previous cervical surgery, multiple gestation, traumatic vaginal delivery, recurrent vaginal infections, connective tissue disorders (e.g., Ehlers-Danlos syndrome and Marfan's syndrome), polycystic ovary syndrome/insulin resistance, and perhaps diabetes. There is debate that a ‘short cervix’ by itself may increase the risk for cervical insufficiency, but if the cervical connective tissue is normal and there is no loss of integrity at the internal cervical os, this seems to be a weak call in many instances.
Whether there is an underlying connective tissue abnormality of the cervix, pathologic activation of the cascade of biochemical events that leads to remodeling of the cervical connective tissue, or simply a congenital or acquired anatomical abnormality of the internal cervical os, the most pathognmonic and sentinel event occurring with cervical incompetence is progressive loss of integrity at the internal cervical os. Cervical change that anticipates labor starts from the inside and progresses outward. Premature cervical ‘remodeling’ can lead to this loss of integrity at the internal os, but it is also often seen in conjunction with congenital uterine malformations (Mullerian defects) that affect midline structures (such as the cervix) and as the consequence of trauma during operative procedures, the most common being D&C. I emphasize this point, because I am a firm believer in the laws of physics with regard to cervical incompetence and its progression, even prior to the connective tissue remodeling (‘ripening’) that will eventually occur once the cervix has been stretched from within.
Let me elaborate on this in the way I explain it to patients: The internal cervical os is supposed to remain closed and basically contiguous with the rest of the inner surface of the uterus – distributing the weight of the baby and fluid over that entire surface area. If the internal os has been damaged and is not closed, or if other factors decrease the resistance at that anatomic site allowing it to begin to open, the tendency will be to simply continue to open, and as that progresses, it actually takes less pressure to continue that process with time. We are talking simple physics here, the same principle that holds when we drive a wedge into a log to split it. It’s hard to get started and then eventually it just gives way.
All women who wear spiked heels should know the reason for this. If you concentrate all the weight of your body, say 150 lbs, on a heel that measures say .2 x .2 inches that translates into a weight of 3750 lbs per square inch! That’s why spiked heels can punch holes in flooring. If we apply that same thinking to pregnancy and the entire volume of the uterus is focused on a weak point, a defective and slightly opened internal cervical os, the tendency is to enlarge that opening and eventually squeeze the membranes into the cervical canal – an event we call cervical funneling – just like squeezing a water balloon through a small opening. The important thing to recognize is that we CAN detect loss of integrity at the internal os during pregnancy by ultrasound and evaluate the configuration of the cervical canal as it begins to distend with membranes and amniotic fluid BEFORE this is readily apparent by clinical symptoms or obvious changes evaluable by vaginal examination of the patient. And this sometimes gives us an opportunity to intervene in a way that can prolong and preserve a pregnancy that might have otherwise been lost or accompanied by extreme prematurity and its attendant morbidity....
Labels: cerclage, cervical incompetence
10 Comments:
At Mon Aug 25, 05:40:00 AM 2008,
Anonymous said…
Dr. Trofatter,
I am 34 weeks pregnant. A few days ago, I was diagnosed with BV and treated with Clindesse. I was also found to be 1-2 cm dilated with a slightly bulging bag. I was given steroid shots for lung development and started on Procardia XL. I am on modified bed rest and permitted to work at my office job half days. Is this a sufficient treatment approach? Is there anything else I should ask to be done?
Thank you!
Hoping not to deliver early.
At Mon Aug 25, 06:27:00 PM 2008,
Kenneth F. Trofatter, Jr., MD, PhD said…
To anonymous: Hard to say! Is this your first pregnancy? Have you had other pregnancies? Any with early deliveries? Is the baby normally grown? Have you had contractions or 'silent' cervical change? Do you have any signs of preeclampsia? Urinary tract infections? Group B Strep? If this is your first baby and you are already having the cervical changes you describe, you probably will deliver early - but it impossible to say at this point if that is one day or 3 weeks from now. Every day you get improves the prospects you will be taking the baby home with you when you leave the hospital. Best of luck and please let us know how things turn out. Dr T
At Mon Aug 25, 08:26:00 PM 2008,
Anonymous said…
In December 05 I was diagnosed with MTHFR C677T Homozygous. I have normal homocystene levels andn negative for anything else. I am now 5 weeks pregnant and am wanting to be delivered by a midwife and not be on all these medications. Do I have to be, or is there a possibility I can do this?
Thanks- Please get back with me!
-Leah
At Tue Aug 26, 05:33:00 AM 2008,
Anonymous said…
Thank you for your reply! It is my first pregnancy. The baby seems to be growing normally based on my fundal measurements. I have had some Braxton Hicks, but no 'real' contractions that I know of. They had me on the monitor for a while and I had only two very small contractions that I didn't really feel. No UTIs, but I am GBS positive. My BP has been good overall, but I've had quite a bit of swelling and trace protein in my urine. The swelling has gone down dramatically since the modified bed rest (lost 8 lbs. in 4 days!).
At Fri Aug 29, 07:13:00 AM 2008,
Anonymous said…
Dear Dr. Trofatter
I am 35 years old and we just lost our baby at 22 weeks pregnancy. It was my first pregnancy and at 20 weeks I was diagnosed with a short cervix (1.8cm cervix and 1.8cm funneling). I am healthy and I had no risk factors (no DC, no infection etc.). After 3 days on bed rest PROM occured.
Next to the grief for our baby I am terrifide that this could happen again. What are my chances in a next pregnancy? What kind of examinations should be performed before the next pregnancy? Would prophylactic cerclage help?
Thank you so much for answering my questions in advance!
At Wed Sep 03, 11:48:00 AM 2008,
Kenneth F. Trofatter, Jr., MD, PhD said…
To Leah Aug 25: First, why did you have the MTHFR testing done to begin with? Secondly, what medications are you taking? Let me know and I will tell you what I think! Dr T
At Wed Sep 03, 11:52:00 AM 2008,
Kenneth F. Trofatter, Jr., MD, PhD said…
To anonymous Aug 29: There is a very high likelihood that you do have an incompetent cervix based on that history. Although there is no good "test" between pregnancies that would relaibly establish that diagnosis, I would suggest a sonohysterogram to evaluate the shape of the uterine cavity and to rule out a congenital uterine (Mullerian) anomaly. My recommendation for another pregnancy would be to have a cerclage placed at 13 weeks after having combined first trimester screening for fetal chromosomal abnormalities. It is much safer to do this than to await significant cervical changes that would make placement of a cerclage much riskier later in the pregnancy. Dr T
At Sat Oct 18, 05:06:00 PM 2008,
Di said…
Dear Dr Trofatter,
I am 9weeks pregnant with my 7th pregnancy - having lost babies due to CI prior to diagnosis. I have one daughter now and had a suture put in with that pregnancy just before 12 weeks and managed to just hold onto that pregnancy as the membranes bulged into the cervix which had shortened and opened at the top at 20wks. I was placed in hosptial for the remainder of confinement and placed head down and on strict bedrest. Luckily the suture held and enabled us to get to 37.5 wks when I delivered her. I am worried because this time the cervix is already slightly open at the internal os and I am 3cm length and the cervix now has some scar tissue from last suture. I am having a suture put in again at 12weeks with this pregnancy but am concerned about if anything can happen before that(i.e can the cervix open up/membranes bulge down) prior to 12 week suture going in??
Would appreciate your reply when time permits.
Kind regards
Di
At Wed Oct 22, 04:41:00 PM 2008,
Kenneth F. Trofatter, Jr., MD, PhD said…
Di: It is extraordinarily rare for the cervix to change significantly before 13-14 weeks. In fact, I have rarely seen cases before 16 weeks. Good luck with the rest of the pregnancy. Hope things go well! Dr T
At Wed May 13, 06:26:00 AM 2009,
mom2many said…
Last year I lost a baby at 20 weeks and 4 days due to incompetent cervix. Which was a total shock considering I had had 5 previous pregnancies with NO complications at all. With that pregnancy I just started bleeding and went to the ER, we was out of town, 4 hours, and seen the available doctor there. He told me I was dialated a 1 and my membranes was bulging. He ended up inducing me saying there was nothing they could do to save the baby. He even ended up rupturing my water and gave me meds to start contractions. I was having NO preterm contractions, or anything to let me know I was in labor. Just had the bleeding.
Now I am 20 weeks and 4 days pregnant again. They told me I "might" have a incompetent cervix after I lost my last child but if I got pregnant again they would keep an eye on things to see. Which really they didnt. My doctor told me that he would have my cervix measured at my ultrasound which was my 2nd trimester one, and was preformed at 19 weeks and 3 days. I thought they would check earlier than that based on stories I have read but at my u/s sure enough my cervix had began to shorten. It was a 2.1 cm. They didnt say nothing about me being dialated so I am not for sure if I was dialated or not. Anyway, they sent me straight to the hospital and set me up for a clerage. I got it within another 2 hours.
After the procedure the doctor seemed happy about the way things went. No complications or anything. I didnt even experience any bleeding or cramping then or later. So I was wondering, with me having my cerclage done at 19 weeks, I read most get it done alot earlier and it does put me at a higher risk for having it done later, but with me still having some cervix and having no contractions, or history of preterm contractions, or even a history of membranes rupturing preterm, is that a good sign for me? I had the McDonald cerclage,btw. I know some of the risk for cerclage is the stitches tearing or pressure breaking it apart. how likely is this to happen? Would I have ANY signs to look for "before" it started? Such as lots of pressure. Or would it just happen really fast. Or more like gradually over a couple days. How successful is the cerclage I got with my situation? Are there any signs I should look for and if so for what? What other problems can occur?
I have tons of questions and no answers. My doctor doesnt want to seem to answer them cause he is always in a hurry and asks as if I am crazy for worrying so much. Even after losing a child! I am looking for any advice and hopefully get some questions answered. If you can answer ANY of my questions, give me ANY advice, I would really appreciate it! Thanks!
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