Anatomy of pregnancy and birth - cervix

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.

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.

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.