Anatomy of pregnancy and birth - uterus
6-minute read
Key facts
- Your uterus (also known as your womb) sits in the middle of your pelvis.
- There are several changes you can expect your uterus to undergo during pregnancy.
- The size of your uterus is monitored during pregnancy.
- During labour, your uterus contracts regularly to open your cervix and help your baby move down into the birth canal.
- Your uterus will continue to have contractions after the birth is completed, whether you had a vaginal or caesarean birth.
What is the uterus?
Your uterus (also known as your womb) sits in the middle of your pelvis. It is pear-shaped and has 3 main sections:
- the fundus (top of the uterus)
- the main body of the uterus
- the cervix (lower part of the uterus)
Ligaments (bands of tough, flexible tissue) hold your uterus in position. It sits behind your bladder and in front of your rectum.
Your uterus wall is made up of 3 layers.
- An inner layer called the endometrium, which responds to hormones. The shedding of this layer is what happens during your periods.
- A middle layer that is muscle.
- A thin outside layer.
How big is the uterus?
The size of a non-pregnant uterus can vary, depending on your age and stage of life. The size and shape of your uterus can also change after pregnancy.
How does my uterus change during pregnancy?
During pregnancy, your uterus houses and nurtures your growing baby. There are several changes you can expect your uterus to undergo during pregnancy. As your baby grows, the size of your uterus will dramatically increase.
Fundal height
At each antenatal visit from about 20 to 24 weeks onwards, your doctor, obstetrician or midwife will measure your fundal height.
Fundal height is the distance from your pubic bone to the top of your uterus.
Several factors can affect the size of your uterus. For instance, the fundal height may be different in people:
- who are carrying more than one baby
- who are overweight or obese
- who have certain medical conditions
A smaller than expected fundal height could be a sign that your baby is growing slowly or that there is too little amniotic fluid. If so, this will be monitored carefully by your doctor.
In contrast, a larger than expected fundal height could mean that your baby is larger than average and this will also need monitoring.
If there are concerns about your baby’s growth, your doctor or midwife may recommend using ultrasound scans to monitor your baby.
How does the uterus prepare for labour and birth?
Braxton Hicks contractions, also known as 'false labour' or 'practice contractions', help prepare your uterus for the birth. These may start early in your pregnancy, but you may not feel them until mid-way through. They continue right through to the birth.
Braxton Hicks contractions tend to be irregular. While they aren’t generally painful, they can be uncomfortable. They can get progressively stronger throughout your pregnancy.
What happens to my uterus during labour?
During active labour, the muscles of your uterus contract to:
- open your cervix
- help your baby move down into the birth canal
Labour contractions start like a wave and build in intensity. The contractions move from the top of the uterus right down to the cervix. Your uterus will feel tight during the contraction. Between contractions, the intensity will ease off and allow you to rest before the next contraction builds.
Unlike Braxton Hicks, labour contractions become stronger, more regular and more frequent in the lead up to giving birth.
How does my uterus change after birth?
If you have a vaginal birth, your uterus will contract again to deliver the placenta. This is sometimes called the ‘after birth’. These contractions are milder than the contractions felt during labour.
If you have a caesarean birth, your baby and the placenta are delivered through a cut in your tummy and the wall of your uterus. This is then stitched up and will form a scar.
Your uterus will continue to have contractions after the birth is completed. This happens whether you had a vaginal birth or a caesarean birth. You may notice this during breastfeeding.
The contracting and tightening of the uterus will feel a little like period pain and is also known as 'afterbirth pains'. These contractions help the uterus to reduce in size.
Read more here about the first few days after giving birth.
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