Why Do We Even Have a Cervix?

Your cervix spends most of its life deciding what gets into and out of your uterus. But what exactly is it, and why do we even have one?

First, what even is the cervix?

The cervix is the lower part of the uterus that connects it to the vagina.¹ Think of it as a small doorway between the two.

But unlike an ordinary doorway, the cervix changes depending on what your body needs.²

The Gatekeeper

One of the cervix’s most important jobs is protection. The vagina naturally contains microorganisms and is also exposed to the outside world. The uterus, on the other hand, needs a more protected environment.

Sitting between the two, the cervix helps create a barrier. Its mucus and local immune defenses help limit potentially harmful microorganisms from travelling upward into the uterus.²˒³

But this barrier isn’t always so difficult to cross.

Around ovulation, hormonal changes alter cervical mucus, making it easier for sperm to travel through.²˒⁴ The same barrier that usually makes passage more difficult becomes more welcoming when pregnancy is possible.

The Fertility Switch

Have you ever noticed that your discharge becomes clearer, wetter or even a little stretchy at certain times of the month?

That isn’t random. Much of what you are noticing around ovulation is cervical mucus, and it is changing for a reason.⁴

As ovulation approaches, levels of a hormone called estrogen rise. This changes the amount and consistency of cervical mucus, making it easier for sperm to move through. Outside of ovulation, the mucus changes again and becomes more difficult for sperm to pass through.²˒⁴˒⁵

So that change in discharge you might notice throughout the month? It can actually be a visible sign of your hormones changing your cervix and your chances of becoming pregnant.

The Pregnancy Protector

Once pregnancy begins, the cervix has a different job.

During pregnancy, the cervix stays closed while its mucus becomes thick and forms what is known as the mucus plug. This creates another layer of protection between the vagina and the uterus, helping prevent harmful microorganisms from travelling upward.³˒⁶

As the body prepares for birth, the cervix begins to soften and change, and the mucus plug may loosen or come away.⁶˒⁷

Instead of helping sperm get in, the cervix is now helping protect what is already inside.

The Doorway for Birth

When it is time for birth, the cervix changes again.

As labour approaches, the cervix becomes softer, shorter and thinner. This thinning and shortening is called effacement. Hormones and other chemical signals in the body, including prostaglandins, help prepare the cervix for this process.⁷˒⁸

The cervix then begins to open, or dilate. This is what healthcare providers mean when they say someone is “4 centimetres dilated” or “8 centimetres dilated.”

During labour, the cervix can eventually reach about 10 centimetres, allowing the baby to pass from the uterus into the vagina.⁹

What About Pap Smears?

For many people, a Pap test may be one of the only times they really think about their cervix.

During a Pap test, cells are collected from the cervix and checked for abnormal changes that could potentially develop into cervical cancer.¹⁰ Many of these changes are linked to HPV (human papillomavirus), a very common infection that usually clears on its own. However, certain high-risk types can persist and cause abnormal cervical cells.¹¹

Today, HPV testing is increasingly used for cervical screening and is recommended by the World Health Organization as the preferred primary screening method.¹² A positive HPV test does not mean you have cervical cancer.

So… Why Do We Even Have One?

The cervix may be small, but it has a surprisingly complicated job.

It helps protect the uterus, changes its mucus to help sperm around ovulation, helps protect a pregnancy, and eventually opens to allow a baby to pass through during birth.

In other words, the cervix isn't simply the bottom of the uterus.

It is a changing gateway: sometimes making it harder for things to get through, sometimes helping them through, and sometimes opening completely.

For an organ we rarely talk about outside of cervical screening, it is doing quite a lot.

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