What is the cervix?
The cervix is the narrow, lower part of the uterus that connects it to the top of the vagina. It has a small opening, the cervical os, that lets period blood out and sperm in. The cervix makes cervical mucus, changes position through the cycle, and widens during labor so a baby can be born.
What it does in your cycle
- Lets period blood out through the cervical os during your period
- Makes [cervical mucus](/glossary/cervical-mucus), which turns slippery near ovulation and thick afterward
- Moves and softens: see cervical position
- Acts as a gatekeeper: thick mucus helps keep bacteria out of the uterus
In pregnancy and birth
During pregnancy a mucus plug seals the cervix. Near labor, the cervix softens, shortens (effaces) and opens (dilates) to about 10 cm so the baby can pass through.
Why it matters for your health
Cells on the cervix can change because of HPV, a very common virus. Most changes clear on their own, but some can slowly develop into cervical cancer. That's why regular cervical screening and the HPV vaccine matter so much: screening catches changes years before they become a problem.
The cervix can also be the source of bleeding between periods or after sex, for example from inflammation, a polyp or infection. A quick exam usually finds the reason.
See a doctor about bleeding after sex, bleeding between periods or after menopause, unusual discharge, or pelvic pain. Keep up with screening even if you feel well, because early cervical changes don't cause symptoms.
Frequently asked questions
How long is the cervix?
Usually about 2.5 to 3.5 cm (around an inch to an inch and a half) long, though it varies and shortens near labor.
Can a tampon or menstrual cup go through the cervix?
No. The opening is far too small. A tampon or cup stays in the vagina.
Does the cervix change with age?
Yes. After childbirth the opening often looks more like a slit, and after menopause the cervix may become smaller and firmer.
Sources
This page is for information only and isn鈥檛 medical advice. If something worries you, please talk to a doctor.
Keep reading
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.Cervical os: definition and meaningThe cervical os is the opening of the cervix. Where it is, how it changes around ovulation and in pregnancy, and why doctors check if it is open.
Cervical screening (Pap test): what it meansCervical screening, the Pap or smear test, checks the cervix for HPV and cell changes. What happens, how often you need it, and the best time in your cycle.
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.