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Anatomy of pregnancy and birth - cervix

5-minute read

Key facts

  • Your cervix is the muscular channel or opening that runs from your uterus (womb) to your vagina.
  • From conception until just before birth, your cervix protects your growing baby. It helps to keep them safe and secure in your uterus.
  • Your cervix undergoes dramatic changes during labour in a process known as ‘effacement’ or ‘ripening’.
  • During labour your cervix dilates (opens) so that your baby can be born.

What is the cervix?

Your cervix is the muscular channel or opening that runs between your uterus (also known as the womb) and your vagina.

Your cervix is found in your pelvis. It sits behind your bladder and in front of the rectum. It is held in position by tough, flexible ligaments.

Diagram showing the female reproductive system.
Illustration showing the female reproductive system.

What does my cervix do?

Your cervix contains a channel, referred to as the 'cervical canal'. Sperm can enter your uterus via this channel. Menstrual blood leaves your uterus through this channel.

The cervix undergoes subtle changes throughout the menstrual cycle when you are not pregnant.

When you ovulate, your cervix secretes mucus that is stretchy and elastic. This type of mucus makes it easier for sperm to reach an egg and be fertilised.

When you aren’t ovulating, the mucus changes to a thicker consistency. This makes it more difficult for sperm or microbes to reach your uterus.

What does my cervix do during pregnancy?

Your cervix plays a crucial role during pregnancy. From conception until just before birth, it protects your growing baby.

From the start of pregnancy, the mucus on the surface of your cervix becomes sticky and thick. This forms a mucus ‘plug’, which helps stop microorganisms, germs such as bacteria and viruses, from entering your uterus and potentially harming your baby.

What problems can occur with my cervix during pregnancy?

Some women have a short cervix (short cervical length) during pregnancy. This can be found during a routine pregnancy ultrasound scan. Having a short cervical length can increase your risk of premature labour and birth (having your baby before 37 weeks of pregnancy).

If you have a short cervical length during pregnancy, your doctor may recommend treatment to reduce your risk of preterm birth. They will also closely monitor your cervix during your pregnancy.

How does my cervix change during labour?

Your cervix undergoes dramatic changes during labour. This is called ‘effacement’ or ‘ripening’. Your cervix changes from long and firm to being soft, thin and more elastic. Your cervix also starts to dilate (open).

Changes to your cervix are partly triggered by contractions of your uterus, which help open the cervix. As your cervix begins to open, you may see a clear, pink, slightly bloody discharge or spotting (sometimes referred to as the 'show'). You may also notice the release of the mucus plug from your cervical canal.

The time it takes for your cervix to open (or dilate) during the first stage of labour will vary between people.

In the 'active phase' of labour, your cervix dilates to approximately 8cm. This is followed by the ‘transition phase’ when your cervix becomes fully open (referred to as being 'fully dilated').

The second stage of labour is when your baby is being born. The third stage of labour is when the placenta is delivered.

is complete when the cervix is fully open (referred to as 'fully dilated'), the baby moves through the pelvis and the mother can begin pushing the baby out. Being fully dilated might not actually be a 10cm opening of the cervix. Rather it is when the doctor or midwife cannot feel any cervix when they perform a vaginal examination.

Illustration showing how the cervix dilates during labour.
Illustration showing how the cervix dilates during labour.
Illustration showing how the cervix dilates during labour.
Illustration showing how the cervix dilates during labour.

Inducing labour

Doctors sometimes recommend that labour is induced (started with medical treatment). Treatment can be given to artificially ripen your cervix. This can be done in several ways to start your labour.

Speak to a maternal child health nurse

Call Pregnancy, Birth and Baby to speak to a maternal child health nurse on 1800 882 436 or video call. Available 7am to midnight (AET), 7 days a week.

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Last reviewed: January 2023


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Need more information?

Labour & birth: what to expect | Raising Children Network

Early labour signs include a show, waters breaking and pain. During labour, your contractions increase and your cervix dilates, so you can birth your baby.

Read more on raisingchildren.net.au website

Short cervix in pregnancy

The cervix is part of the female reproductive system. People with a short cervix have a higher than average risk of giving birth early.

Read more on Pregnancy, Birth & Baby website

Preterm labour - MyDr.com.au

Going into labour before your 37th week of pregnancy is called preterm labour, or premature labour. Find out what it means for you and your baby.

Read more on myDr website

Labour complications

Even if you’re healthy and well prepared for childbirth, there’s always a chance of unexpected problems. Learn more about labour complications.

Read more on Pregnancy, Birth & Baby website

Induction of labour

Induction of labour is when labour is started with medical treatment. Read about the reasons why you may be induced and the different methods used.

Read more on Pregnancy, Birth & Baby website

Slow progress in labour

Slow progress in labour is also called failure to progress or prolonged labour. Read what happens when your labour doesn't go as quickly as expected.

Read more on Pregnancy, Birth & Baby website

Giving birth - second stage of labour

The second stage of labour lasts from when the cervix is fully dilated (open) until your baby’s birth. Learn more about this stage.

Read more on Pregnancy, Birth & Baby website

Induction of Labour

Read more on RANZCOG - Royal Australian and New Zealand College of Obstetricians and Gynaecologists website

Interventions during labour

An 'intervention' is an action taken by a midwife or doctor to help you birth your baby safely.

Read more on Pregnancy, Birth & Baby website

Stretch and sweep

A ‘stretch and sweep’ or ‘membrane sweep’ is a relatively gentle way of trying to start labour. Find out what it involves and its benefits and risks.

Read more on Pregnancy, Birth & Baby website

Call us and speak to a Maternal Child Health Nurse for personal advice and guidance.

Need further advice or guidance from our maternal child health nurses?

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