Thanks to television shows like “Friends,” many of us were familiar with the concept of cervical dilation even before we became moms (although, if I’m being honest, I didn’t really stop to consider just how much 10 centimeters was until I was pregnant!). For many of us, only when we start counting down the days until our first baby’s due date do we start really learning how our bodies prepare for—and progress through—the labor and delivery process. In particular, we start hoping to hear promising news about cervical dilation and effacement at those last doctor’s appointments. But can a cervical check predict the start of labor?
Effacement and dilation
“Effacement” is a term referring to the way the cervix stretches, becoming softer, shorter, and thinner, before and then during labor. It occurs when the baby’s head drops and pushes against the cervix and is described as a percentage—such as “30% effaced.” Once the cervix begins to thin, it also starts to open—what is called “dilation.” While most of the dilation happens during labor itself, both effacement and dilation can begin weeks before labor starts. Starting at 37 weeks gestation, your healthcare provider may offer to check your dilation, which involves an exam during which he or she can also verify that the baby is head down (though a cervical check isn’t the only way to know if your baby is head down). These checks before labor starts may be very painful.
Does how dilated you are tell you when labor will start?
When my OB/GYN offered to do a cervical check at 39 weeks, I decided that the potential discomfort or pain of a cervical check would be worth it to know whether the discomfort and pain of the third trimester would be over soon (despite the fact that I knew it may not even be able to tell me much). Unfortunately, my OB/GYN is a doctor, not a psychic, and I hadn’t progressed enough for him to be able to give me any indication of when labor would happen.
As health economist Emily Oster notes in her 2014 book Expecting Better, cervical effacement, more so than dilation, may give some clue about how much longer you have left to wait until you meet your baby. She writes: “The state of the cervix does have some predictive power, especially on or after your due date” (my cervical check was before my due date). She notes that a study from the U.K. found that “for women who were more than 60 percent effaced (that means shortened about halfway) at 37 weeks, almost all of them (something like 98 percent) went into labor before their due date. On the other hand, for women who were less than 40 percent effaced, almost none of them (less than 10 percent) went into labor before their due date.”
Your Bishop score is a better indicator of when labor will start than cervical dilation alone
Oster recommends that a woman makes sure to ask her provider about effacement if he or she only mentions dilation, since it’s a better predictor of when the woman will go into labor. Asking about the Bishop score—a number that includes not just effacement and dilation, but also the cervix’s position and the position of the baby—in addition to effacement, might be helpful as well.
The Bishop score and effacement percentage can also help women who are induced to avoid a C-section, because “the more ready you are, the more likely the induction will lead to a vaginal delivery,” Oster notes. So, if a woman is “considering a medical induction” but wants to try to avoid a C-section, knowing her Bishop score can help.
Cervical checks may give expectant moms false hope about the timing of labor starting or how fast labor will progress
Because dilation alone doesn’t tell us much about when labor will begin, unfortunately, cervical checks can also cause false hope for a woman longing to be finished with pregnancy and meet her baby! Many of us have heard stories of women who were a few centimeters dilated for weeks or, on the flip side, of women who were told at their 40-week appointment that they weren’t even close, and then went into labor later that same day.
First-time mothers, in particular, may not even begin dilating until active labor. For these reasons, and for the increased risk of infection, you may want to opt out of “routine” cervical checks at your pre-due date OB appointments altogether (generally, cervical checks at appointments on or after your due date are no longer optional—however, your provider should always request your consent before any exam or procedure!).
When do you need a cervical check?
So, why have a cervical check during pregnancy? According to an article by Dr. Stephanie McNally and Patricia Scanlon, a cervical check is necessary if you are having symptoms of labor (pain, bleeding, or a clear or pink sticky discharge) or if you are going to be induced, either for medical reasons or by choice. Again, the further dilated you are when you are induced, the less likely you are to need a C-section.
You’ll also receive a cervical check when you arrive at your hospital or birthing center and again later during labor, to ensure you’re ready to push. By then, though, that information is much more meaningful.
Ultimately, your provider should only offer a cervical check at a prenatal exam, not demand one be performed—and you can say yes or no. If you have any questions about the risks and benefits it will provide you individually, be sure to ask.
Lastly, hang in there! No one stays pregnant forever. You’ll be holding your baby soon.