Do You Know What the Cervical Os Is?

During pregnancy, you may hear doctors refer to the cervical os. What is it and what does it do?

doctor with blue gloved hands points to Cervical opening on cervix model with pointer

Illustration by Jaelen Brock

The female reproductive system is complex. Many women still aren't entirely confident about how the whole thing works. In fact, during pregnancy, some women might learn about parts of the reproductive system they've never heard of. That could include the cervical os.

A healthy cervical os dilates at the correct times: during menstruation, ovulation and labor.

The cervical os is a small but vital part of a woman's reproductive system. We spoke to Gareth Nye, B.Sc., Ph.D., to better understand how it works and why it becomes so important during pregnancy and menstruation.

What is the cervical os?

"The cervical os are the two cervical openings present at either the uterus-facing side (internal os) or the vagina-facing side (external os)," said Nye, a senior lecturer at Chester Medical School at the University of Chester in the United Kingdom. "They form the two ends of the endocervical canal, which can vary between 2 and 3 centimeters in length."

The cervix plays a vital role during pregnancy. It helps hold the baby in the uterus and holds the mucus plug, which provides a layer of security between the uterus and the external world.

What is the function of the cervical os?

Since the two openings of the cervical os connect the cervix to the rest of the reproductive system, they play a vital role in both menstruation and pregnancy.

"Clearly, the cervical canal is needed to allow substances in and out of the uterus," Nye said. "During menstruation, this is the shed lining of the uterus wall or the endometrium. During pregnancy, it remains shut to stop any damage to the growing baby."

The cervical os also dilates during labor. As labor begins and the cervix begins to dilate, the mucus plug in the cervical os will loosen and release a layer of thick mucus out of the vagina.

To accommodate the baby's movement out of the uterus and down the birth canal, a woman's cervix becomes softer and usually dilates to 10 cm.

FAQs about the cervical os

What are some problems associated with cervical os?

A healthy cervical os dilates at the correct times: during menstruation, ovulation and labor. However, some women have what is known as cervical stenosis.

Cervical stenosis, or a tight cervix, means that the cervical os struggles to fully dilate. In some cases, the cervix may be completely closed.

"This is commonplace during menopause because the tissues get narrower and weaker with age and change in hormonal profiles," Nye said. "You can also get this condition with cervical cancers or the treatment of cancers."

The result may be painful periods, fertility problems and difficulties during labor. If you experience symptoms, your doctor may recommend a procedure that widens the cervix.

Cervicitis, or the inflammation of the cervix, is another issue that can cause complications with the cervical os. The cervical os can become inflamed as a result of a sexually transmitted infection (STI).

Symptoms include pain in the upper vagina and uterus, bleeding between periods and abnormal discharge.

"You may have been born with congenital conditions which alter the anatomy of your cervix, which may also lead to issues, although this wouldn't be obvious without examination," Nye said.

Can you feel your own cervical os?

Yes, it is possible (and sometimes practical) to feel your cervix. Insert a finger into the vagina and feel for a raised circle with a tiny gap or dimple in the center. This is your cervical os.

Knowing how to feel your cervical os is a helpful way to determine whether you are ovulating, as the cervix tends to feel higher, softer and wetter during this phase of the menstrual cycle.