Vaginal exams. I don't know a single woman who likes them.
However, there is a myth perpetuated in our society that vaginal exams at the end of pregnancy are beneficial. The common belief is that by doing a vaginal exam one can tell that labor will begin soon. This is not the case.
Most practitioners will do an initial vaginal exam at the beginning of pregnancy to do a pap smear, and other testing. Then they don't do any until about the 36 week mark, unless complications arise that call for further testing or to assess the cervix. If your practitioner wants to do a vaginal exam at every visit, you should probably question them as to why.
Vaginal exams can measure certain things:
Dilation: How far your cervix has opened. 10 centimeters being the widest.
Ripeness: The consistency of your cervix. It starts out being firm like the tip of your nose, softening to what your ear lobe feels like and eventually feeling like the inside of your cheek.
Effacement: This is how thin your cervix is. If you think of your cervix as funnel-like, and measuring about 2 inches, you will see that 50% effaced means that your cervix is now about 1 inch in length. As the cervix softens and dilates the length decreases as well.
Station: This is the position of the baby in relation to your pelvis, measured in pluses and minuses. A baby who is at 0 station is said to be engaged, while a baby in the negative numbers is said to be floating. The positive numbers are the way out!
Position of the baby: By feeling the suture lines on the skull of the baby, where the four plates of bone haven't fused yet, one can tell you which direction the baby is facing because the anterior and posterior fontanels (soft spots) are shaped differently.
Position of the cervix: The cervix will move from being more posterior to anterior. Many women can tell when the cervix begins to move around because when a vaginal exam is performed it no longer feels like the cervix is located near her tonsils.
Labor is not simply about a cervix that has dilated, softened or anything else. A woman can be very dilated and not have her baby before her due date or even near her due date. I've personally had women who were 6 centimeters dilated for weeks. Then there is the sad woman who calls me to say that her cervix is high and tight, she's been told that this baby isn't coming for awhile, only to be at her side as she gives birth within 24 hours. Vaginal exams are just not good predictors of when labor will start.
Using a vaginal exam to predict advisability for a vaginal birth is usually not very accurate, for several reasons. First of all it leaves out the factor of labor and positioning. During labor it's natural for the baby's head to mold and the mother's pelvis to move. If done in early pregnancy it also removes the knowledge of what hormones like Relaxin will do to help make the pelvis, a moveable structure, be flexible. The only real exception to this is in the case of a very oddly structured pelvis. For example, a mother who was in a car accident and suffered a shattered pelvis or someone who might have a specific bone problem, which is more commonly seen where there is improper nutrition during the growing years.
During labor vaginal exams can't tell you exactly how close you are either, so keeping them to a minimum then is also a good idea, particularly if your membranes have ruptured.
Okay, so there's not really a great reason to have a vaginal in exam done routinely for most women. So are there any reasons not to have vaginal exams? There sure are.
Vaginal exams can increase the risks of infection, even when done carefully and with sterile gloves, etc. It pushes the normal bacteria found in the vagina upwards towards the cervix. There is also increased risk of rupturing the membranes. Some practitioners routinely do what is called stripping the membranes, which simply separates the bag of waters from the cervix. The thought behind this is that it will stimulate the production of prostaglandins to help labor begin and irritate the cervix causing it to contract. This has not been shown to be effective for everyone and does have the aforementioned risks.
In the end only you and your practitioner can decide what is right for your care in pregnancy. Some women refuse vaginal exams altogether, so request to have them done only after 40 weeks, or every other week or whatever she feels comfortable with.