Internal/External Os

Specialties Ob/Gyn

Published

Can anyone help explain cervical checks in relation to internal and external os? I know conceptually that there is both and that there is supposed to be a tunnel from the external to the internal which gives you your measure of effacement but I cant say that I have ever felt it! When I have done cervical checks I have gone in, felt the ring of the cervix and just felt how thick the cervix felt there in the ring and I usually feel something hard (babys head) right there as well. My preceptor informed me that no, that is the external os and you have to actually push up on baby's head to feel the internal os. I dont know, I cant say I completely understand this. If the internal os is smaller then why do I feel the babys head at the external os (I would think it would not come down if the internal is smaller). Can anyone help me figure this out a little better? I have had a hard enough time feeling one os let alone two!

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Specializes in OB-Gyn/Primary Care/Ambulatory Leadership.

If the patient is more than 50-75% effaced, differentiating between internal and external os is not really all that important. I generally only feel it if the patient is really thick still, and not extremely soft. In that case, you might have an external os of 2cm (where you can easily get your whole index finger into it, but as you move further in, it funnels somewhat, and you cannot get your entire finger through the other side (which might then indicate that the internal os is only a fingertip).

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Specializes in L&D.

Rarely you will encounter a situation where the cervix seems to be dilated to 6 cm, but on further investigation, you find a 2cm opening posterior to what you first felt. That 2cm opening is usually paper thin. Picture a 2cm circle in the center of a 6cm circle. This is an extreme example of feeling both the internal and external os. What Klone described above is the more usual situation.

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It is more obvious when the pt's cervix is thick. When you go to check, you feel the outer os first and it might feel like 2 cm, then when you tunnel your fingers through, you notice the internal os only fingertip.

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Specializes in OB.

I agree with everyone else. Usually you will only feel an internal and external os when the cervix is thicker. I'm not sure what your preceptor is talking about. In the beginning , just focus on finding the internal os. Don't worry about the external for now. That will come with experience!

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Thank you for your replies. :) I know the topic of cervical checks has been beaten to death but I imagine it is such a hot topic because it can be so difficult. If you don't mind, I'd like to describe how I do it/what goes through my mind and maybe you all could tell me what I'm missing in my thought process ?? So basically, I go in and the first thing I'm searching for is the cervix which I deem to be something that feels like an open circle amidst all the mush! I really wish I knew anatomically what all that mush was that I am feeling so that I could find my way better! Anyway, once I find the circle of the cervix (if I ever do) then I feel what is in the middle of it which usually feels like something hard like the baby's head. Once that is done I gently open my fingers from one side of the cervical opening to the other (being careful not to stretch the cervix for accuracy) and measure how far dilated. I have honestly never felt a long tunnel of thick cervix. All I have ever felt so far is cervix lying on the head of the baby so I have just measured how thick the rim is basically, for effacement. No one ever seems to be able to explain cervical checks on my unit. I have researched every thing I know how to and I know I need experience. Is what I described the correct way in your estimation?

Thank you so much for your expertise!

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Specializes in OB.

It sounds like you just need more practice. Your technique sounds good. I would say any chance you get, check a cervix, even if it is not your patient. Try to check a closed thick cervix, a swollen cervix, a cervix with scar tissue from a LEEP, etc. Practice, practice, practice...it will get easier. If you work in a small hospital, this will be a little harder, but eventually it will click. Don't feel bad, it takes everyone a while to catch on. I felt like I was never going to get it and then one day, it just clicked!

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Specializes in L and D.

It takes lots and lots if practice. One thing ive realized in my years of practice too is that a woman not really in labor and not with an epidural can really clench down on you and make a cervical check difficult. Sometimes if i didnt know any better i'd bet that the woman i checked before an epidural ( where she is not relaxed and makes it very near impossible to check) is NOT the same woman i am checking after. Once they relax, their anatomy can feel completely different

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I am happy to report that at work yesterday I had my chance to check another cervix. I used what I learned and all your comments and found it! Not only that, I feel for the first time that I knew more comprehensively what I was looking for and I got the assessment right! I had another nurse check after me to make sure. Thanks so much for your help and encouragement. One down, 1000's to go!

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