Cervical os: definition and meaning
The cervical os is the opening in the center of the cervix, the narrow passage between the vagina and the uterus. The external os opens into the vagina and the internal os opens into the uterus. Menstrual blood flows out and sperm travel in through it. It softens and opens slightly around ovulation and during a period.
External and internal os
| Part | Where | Role |
|---|---|---|
| External os | the end of the cervix you could feel in the vagina | lets period blood out and sperm in |
| Cervical canal | the short tunnel between the two openings | lined with mucus-making glands |
| Internal os | where the canal meets the uterus | stays closed during pregnancy to hold it in |
Before a vaginal birth, the external os is often a small round dot. Afterward it usually looks more like a short slit.
How the os changes across the cycle
Around ovulation, rising estrogen makes the cervix higher, softer, wetter and the os slightly more open, to help sperm through. After ovulation it becomes firmer, lower and more closed. Some people track this as cervical position, alongside cervical mucus.
Why doctors check the os
- In pregnancy: an os that opens too early may need monitoring.
- During a miscarriage: an open os usually means the pregnancy is passing; a closed os with bleeding may be a threatened miscarriage. See miscarriage.
- In labor: dilation of the os is measured up to 10 cm.
- During screening: the area around the os is where cervical screening samples cells.
Checking your own cervix is optional. If you do, wash your hands, trim nails and go gently. It is fine to skip it and rely on mucus or temperature instead.
Frequently asked questions
Can you feel your cervical os?
Some people can feel a small dimple in the center of the cervix with a clean finger. It is easiest when the cervix sits lower, after ovulation.
Does the cervical os open during a period?
Slightly, so blood can flow out. It is still very small, which is why a tampon cannot pass into the uterus.
Sources
This page is for information only and isn鈥檛 medical advice. If something worries you, please talk to a doctor.
Keep reading
What is the cervix?The cervix is the narrow lower end of the uterus that opens into the vagina. What it does in your cycle, in pregnancy, and why screening matters.Cervical position: definition and meaningCervical position is how high, soft and open your cervix is, which shifts through your cycle. How it changes around ovulation and how to check it.
Cervical mucus: definition and meaningCervical mucus is fluid made by the cervix that changes through your cycle. What each texture means, how it signals ovulation, and what's normal.What are the signs of ovulation?Signs of ovulation: egg-white discharge, a positive LH test, a temperature rise, one-sided twinges and higher sex drive. What each means and how to read them.
Uterus: definition and meaningThe uterus, or womb, is where a period comes from and where a pregnancy grows. Its parts, how it changes each cycle, and common conditions that affect it.